diff --git a/PDTSimpleCalendar/PDTSimpleCalendarViewCell.h b/PDTSimpleCalendar/PDTSimpleCalendarViewCell.h
index 7e41c1c..9da3407 100644
--- a/PDTSimpleCalendar/PDTSimpleCalendarViewCell.h
+++ b/PDTSimpleCalendar/PDTSimpleCalendarViewCell.h
@@ -6,8 +6,10 @@
 //  Copyright (c) 2013 Producteev. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
-#import <UIKit/UIKit.h>
+@import UIKit;
+NS_ASSUME_NONNULL_BEGIN
+
+extern const CGFloat kPDTSimpleCalendarCircleSize;
 
 @class PDTSimpleCalendarViewCell;
 
@@ -34,7 +36,7 @@
  *
  *  @return The text desired color
  */
-- (UIColor *)simpleCalendarViewCell:(PDTSimpleCalendarViewCell *)cell textColorForDate:(NSDate *)date;
+- (nullable UIColor *)simpleCalendarViewCell:(PDTSimpleCalendarViewCell *)cell textColorForDate:(NSDate *)date;
 
 /**
  *  Asks the delegate for the circle color for a specific date.
@@ -45,14 +47,14 @@
  *
  *  @return The circle desired color
  */
-- (UIColor *)simpleCalendarViewCell:(PDTSimpleCalendarViewCell *)cell circleColorForDate:(NSDate *)date;
+- (nullable UIColor *)simpleCalendarViewCell:(PDTSimpleCalendarViewCell *)cell circleColorForDate:(NSDate *)date;
 
 @end
 
 /**
  *  The `PDTSimpleCalendarViewCell` class displays a day in the calendar.
  */
-@interface PDTSimpleCalendarViewCell : UICollectionViewCell
+@interface PDTSimpleCalendarViewCell : UICollectionViewCell <UIAppearanceContainer>
 
 /**
  *  The delegate of the cell.
@@ -65,7 +67,7 @@
 /**
  *  Define if the cell is today in the calendar.
  */
-@property (nonatomic, assign) BOOL isToday;
+@property (nonatomic, assign, getter=isToday) BOOL today;
 
 /**
  *  Customize the circle behind the day's number color using UIAppearance.
@@ -114,7 +116,12 @@
  *
  * @param calendar the calendar.
  */
-- (void)setDate:(NSDate*)date calendar:(NSCalendar*)calendar;
+- (void)setDate:(nullable NSDate*)date calendar:(nullable NSCalendar*)calendar;
+
+/**
+ * Set the text for this cell.
+ */
+@property (nonatomic, strong) NSString *text;
 
 /**
  *  Force the refresh of the colors for the circle and the text
@@ -122,3 +129,4 @@
 - (void)refreshCellColors;
 
 @end
+NS_ASSUME_NONNULL_END
diff --git a/PDTSimpleCalendar/PDTSimpleCalendarViewCell.m b/PDTSimpleCalendar/PDTSimpleCalendarViewCell.m
index 36b01ef..dafce79 100644
--- a/PDTSimpleCalendar/PDTSimpleCalendarViewCell.m
+++ b/PDTSimpleCalendar/PDTSimpleCalendarViewCell.m
@@ -8,7 +8,7 @@
 
 #import "PDTSimpleCalendarViewCell.h"
 
-const CGFloat PDTSimpleCalendarCircleSize = 32.0f;
+const CGFloat kPDTSimpleCalendarCircleSize = 32.0f;
 
 @interface PDTSimpleCalendarViewCell ()
 
@@ -21,6 +21,23 @@ @implementation PDTSimpleCalendarViewCell
 
 #pragma mark - Class Methods
 
++ (void)initialize {
+    if (self == [PDTSimpleCalendarViewCell class]) {
+        // Set the UIAppearance default values.
+        PDTSimpleCalendarViewCell *proxy = [PDTSimpleCalendarViewCell appearance];
+
+        proxy.circleDefaultColor  = [UIColor whiteColor];
+        proxy.circleTodayColor    = [UIColor grayColor];
+        proxy.circleSelectedColor = [UIColor redColor];
+
+        proxy.textDefaultColor  = [UIColor blackColor];
+        proxy.textTodayColor    = [UIColor whiteColor];
+        proxy.textSelectedColor = [UIColor whiteColor];
+        proxy.textDisabledColor = [UIColor lightGrayColor];
+        proxy.textDefaultFont   = [UIFont systemFontOfSize: 17.0];
+    }
+}
+
 + (NSString *)formatDate:(NSDate *)date withCalendar:(NSCalendar *)calendar
 {
     NSDateFormatter *dateFormatter = [self dateFormatter];
@@ -33,7 +50,6 @@ + (NSString *)formatAccessibilityDate:(NSDate *)date withCalendar:(NSCalendar *)
     return [PDTSimpleCalendarViewCell stringFromDate:date withDateFormatter:dateFormatter withCalendar:calendar];
 }
 
-
 + (NSDateFormatter *)dateFormatter {
     static NSDateFormatter *dateFormatter;
     static dispatch_once_t onceToken;
@@ -51,7 +67,6 @@ + (NSDateFormatter *)accessibilityDateFormatter {
         dateFormatter = [[NSDateFormatter alloc] init];
         [dateFormatter setDateStyle:NSDateFormatterLongStyle];
         [dateFormatter setTimeStyle:NSDateFormatterNoStyle];
-        
     });
     return dateFormatter;
 }
@@ -66,34 +81,41 @@ + (NSString *)stringFromDate:(NSDate *)date withDateFormatter:(NSDateFormatter *
 
 #pragma mark - Instance Methods
 
-- (id)initWithFrame:(CGRect)frame
+- (instancetype)initWithFrame:(CGRect)frame
 {
     self = [super initWithFrame:frame];
     if (self) {
         _date = nil;
-        _isToday = NO;
+        _today = NO;
         _dayLabel = [[UILabel alloc] init];
-        [self.dayLabel setFont:[self textDefaultFont]];
-        [self.dayLabel setTextAlignment:NSTextAlignmentCenter];
-        [self.contentView addSubview:self.dayLabel];
+        [_dayLabel setTextAlignment: NSTextAlignmentCenter];
+        [self.contentView addSubview: _dayLabel];
 
         //Add the Constraints
-        [self.dayLabel setTranslatesAutoresizingMaskIntoConstraints:NO];
-        [self.dayLabel setBackgroundColor:[UIColor clearColor]];
-        self.dayLabel.layer.cornerRadius = PDTSimpleCalendarCircleSize/2;
-        self.dayLabel.layer.masksToBounds = YES;
-
-        [self.contentView addConstraint:[NSLayoutConstraint constraintWithItem:self.dayLabel attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.contentView attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0.0]];
-        [self.contentView addConstraint:[NSLayoutConstraint constraintWithItem:self.dayLabel attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.contentView attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0.0]];
-        [self.contentView addConstraint:[NSLayoutConstraint constraintWithItem:self.dayLabel attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:PDTSimpleCalendarCircleSize]];
-        [self.contentView addConstraint:[NSLayoutConstraint constraintWithItem:self.dayLabel attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:PDTSimpleCalendarCircleSize]];
+        [_dayLabel setTranslatesAutoresizingMaskIntoConstraints: NO];
+        [_dayLabel setBackgroundColor:[UIColor clearColor]];
+        _dayLabel.layer.cornerRadius = kPDTSimpleCalendarCircleSize/2;
+        _dayLabel.layer.masksToBounds = YES;
 
-        [self setCircleColor:NO selected:NO];
+        [self.contentView addConstraint: [NSLayoutConstraint constraintWithItem: _dayLabel attribute: NSLayoutAttributeCenterX relatedBy: NSLayoutRelationEqual toItem: self.contentView attribute: NSLayoutAttributeCenterX multiplier: 1.0 constant: 0.0]];
+        [self.contentView addConstraint: [NSLayoutConstraint constraintWithItem: _dayLabel attribute: NSLayoutAttributeCenterY relatedBy: NSLayoutRelationEqual toItem: self.contentView attribute: NSLayoutAttributeCenterY multiplier: 1.0 constant: 0.0]];
+        [self.contentView addConstraint: [NSLayoutConstraint constraintWithItem: _dayLabel attribute: NSLayoutAttributeHeight relatedBy: NSLayoutRelationEqual toItem: nil attribute: NSLayoutAttributeNotAnAttribute multiplier: 1.0 constant: kPDTSimpleCalendarCircleSize]];
+        [self.contentView addConstraint: [NSLayoutConstraint constraintWithItem: _dayLabel attribute: NSLayoutAttributeWidth relatedBy: NSLayoutRelationEqual toItem: nil attribute: NSLayoutAttributeNotAnAttribute multiplier: 1.0 constant: kPDTSimpleCalendarCircleSize]];
     }
-
     return self;
 }
 
+- (void) didMoveToWindow {
+    // Use the UIAppearance properties only after they been finalized by being
+    // inserted into a live window.
+    [super didMoveToWindow];
+
+    if (self.window) {
+        [self.dayLabel setFont: self.textDefaultFont];
+        [self setCircleColor: self.isToday selected: self.selected];
+    }
+}
+
 - (void)setDate:(NSDate *)date calendar:(NSCalendar *)calendar
 {
     NSString* day = @"";
@@ -107,10 +129,23 @@ - (void)setDate:(NSDate *)date calendar:(NSCalendar *)calendar
     self.dayLabel.accessibilityLabel = accessibilityDay;
 }
 
-- (void)setIsToday:(BOOL)isToday
+@dynamic text;
+
+- (NSString *) text {
+
+    return self.dayLabel.text;
+}
+
+- (void) setText: (NSString *)text {
+
+    self.dayLabel.text = text;
+    self.dayLabel.accessibilityLabel = text;
+}
+
+- (void) setToday: (BOOL) today
 {
-    _isToday = isToday;
-    [self setCircleColor:isToday selected:self.selected];
+    _today = today;
+    [self setCircleColor: today selected: self.selected];
 }
 
 - (void)setSelected:(BOOL)selected
@@ -137,144 +172,51 @@ - (void)setCircleColor:(BOOL)today selected:(BOOL)selected
             }
         }
     }
-    
     if (selected) {
         circleColor = [self circleSelectedColor];
         labelColor = [self textSelectedColor];
     }
-
     [self.dayLabel setBackgroundColor:circleColor];
     [self.dayLabel setTextColor:labelColor];
 }
 
-
 - (void)refreshCellColors
 {
     [self setCircleColor:self.isToday selected:self.isSelected];
 }
 
-
 #pragma mark - Prepare for Reuse
 
 - (void)prepareForReuse
 {
     [super prepareForReuse];
-    _date = nil;
-    _isToday = NO;
-    [self.dayLabel setText:@""];
-    [self.dayLabel setBackgroundColor:[self circleDefaultColor]];
-    [self.dayLabel setTextColor:[self textDefaultColor]];
-}
-
-#pragma mark - Circle Color Customization Methods
-
-- (UIColor *)circleDefaultColor
-{
-    if(_circleDefaultColor == nil) {
-        _circleDefaultColor = [[[self class] appearance] circleDefaultColor];
-    }
-
-    if(_circleDefaultColor != nil) {
-        return _circleDefaultColor;
-    }
+    self.date = nil;
+    self.today = NO;
 
-    return [UIColor whiteColor];
-}
+    // TODO: File a Doc bug, Thaddeus Cooper in DTS. Quinn & Larry, Kirby Turner.
+    PDTSimpleCalendarViewCell *proxy = [PDTSimpleCalendarViewCell appearance];
 
-- (UIColor *)circleTodayColor
-{
-    if(_circleTodayColor == nil) {
-        _circleTodayColor = [[[self class] appearance] circleTodayColor];
-    }
+    if (_circleDefaultColor)  { self.circleDefaultColor  = proxy.circleDefaultColor; }
+    if (_circleTodayColor)    { self.circleTodayColor    = proxy.circleTodayColor; }
+    if (_circleSelectedColor) { self.circleSelectedColor = proxy.circleSelectedColor; }
 
-    if(_circleTodayColor != nil) {
-        return _circleTodayColor;
-    }
+    if (_textDefaultColor)  { self.textDefaultColor  = proxy.textDefaultColor; }
+    if (_textTodayColor)    { self.textTodayColor    = proxy.textTodayColor; }
+    if (_textSelectedColor) { self.textSelectedColor = proxy.textSelectedColor; }
+    if (_textDisabledColor) { self.textDisabledColor = proxy.textDisabledColor; }
+    if (_textDefaultFont)   { self.textDefaultFont   = proxy.textDefaultFont; }
 
-    return [UIColor grayColor];
-}
-
-- (UIColor *)circleSelectedColor
-{
-    if(_circleSelectedColor == nil) {
-        _circleSelectedColor = [[[self class] appearance] circleSelectedColor];
-    }
-
-    if(_circleSelectedColor != nil) {
-        return _circleSelectedColor;
-    }
-
-    return [UIColor redColor];
+    self.dayLabel.text = @"";
+    self.dayLabel.backgroundColor =  proxy.circleDefaultColor;
+    self.dayLabel.textColor = proxy.textDefaultColor;
 }
 
 #pragma mark - Text Label Customizations Color
 
-- (UIColor *)textDefaultColor
-{
-    if(_textDefaultColor == nil) {
-        _textDefaultColor = [[[self class] appearance] textDefaultColor];
-    }
-
-    if(_textDefaultColor != nil) {
-        return _textDefaultColor;
-    }
-
-    return [UIColor blackColor];
-}
-
-- (UIColor *)textTodayColor
-{
-    if(_textTodayColor == nil) {
-        _textTodayColor = [[[self class] appearance] textTodayColor];
-    }
-
-    if(_textTodayColor != nil) {
-        return _textTodayColor;
-    }
-
-    return [UIColor whiteColor];
-}
-
-- (UIColor *)textSelectedColor
-{
-    if(_textSelectedColor == nil) {
-        _textSelectedColor = [[[self class] appearance] textSelectedColor];
-    }
-
-    if(_textSelectedColor != nil) {
-        return _textSelectedColor;
-    }
-
-    return [UIColor whiteColor];
-}
-
-- (UIColor *)textDisabledColor
-{
-    if(_textDisabledColor == nil) {
-        _textDisabledColor = [[[self class] appearance] textDisabledColor];
-    }
-
-    if(_textDisabledColor != nil) {
-        return _textDisabledColor;
-    }
-
-    return [UIColor lightGrayColor];
-}
-
-#pragma mark - Text Label Customizations Font
-
-- (UIFont *)textDefaultFont
+- (void) setTextDefaultColor: (UIColor *) textDefaultColor
 {
-    if(_textDefaultFont == nil) {
-        _textDefaultFont = [[[self class] appearance] textDefaultFont];
-    }
-
-    if (_textDefaultFont != nil) {
-        return _textDefaultFont;
-    }
-
-    // default system font
-    return [UIFont systemFontOfSize:17.0];
+    _textDefaultColor = textDefaultColor ?: [[[self class] appearance] textDefaultColor];
+    self.dayLabel.textColor = _textDefaultColor;
 }
 
 @end
diff --git a/PDTSimpleCalendar/PDTSimpleCalendarViewController.h b/PDTSimpleCalendar/PDTSimpleCalendarViewController.h
index 661e056..2ce59ae 100644
--- a/PDTSimpleCalendar/PDTSimpleCalendarViewController.h
+++ b/PDTSimpleCalendar/PDTSimpleCalendarViewController.h
@@ -6,9 +6,10 @@
 //  Copyright (c) 2013 Producteev. All rights reserved.
 //
 
-#import <UIKit/UIKit.h>
+@import UIKit;
 
 #import "PDTSimpleCalendarViewWeekdayHeader.h"
+NS_ASSUME_NONNULL_BEGIN
 
 @protocol PDTSimpleCalendarViewDelegate;
 
@@ -43,7 +44,7 @@
  *  Changing this value will not cause the calendar to scroll to this date.
  *  You need to manually call scrollToSelectedDate:(BOOL)animated if you want this behavior.
  */
-@property (nonatomic, strong) NSDate *selectedDate;
+@property (nullable, nonatomic, strong) NSDate *selectedDate;
 
 /** @name Customizing Appearance */
 
@@ -80,7 +81,7 @@
  *
  *  @see PDTSimpleCalendarViewDelegate
  */
-@property (nonatomic, weak) id<PDTSimpleCalendarViewDelegate> delegate;
+@property (nullable, nonatomic, weak) id<PDTSimpleCalendarViewDelegate> delegate;
 
 
 /**
@@ -144,7 +145,7 @@
  *  @param controller the calendarView Controller
  *  @param date       the date (Midnight GMT)
  */
-- (UIColor *)simpleCalendarViewController:(PDTSimpleCalendarViewController *)controller circleColorForDate:(NSDate *)date;
+- (nullable UIColor *)simpleCalendarViewController:(PDTSimpleCalendarViewController *)controller circleColorForDate:(NSDate *)date;
 
 /**
  *  Asks the delegate for the text color for a custom added date
@@ -152,6 +153,15 @@
  *  @param controller the calendarView Controller
  *  @param date       the date (Midnight GMT)
  */
-- (UIColor *)simpleCalendarViewController:(PDTSimpleCalendarViewController *)controller textColorForDate:(NSDate *)date;
+- (nullable UIColor *)simpleCalendarViewController:(PDTSimpleCalendarViewController *)controller textColorForDate:(NSDate *)date;
+
+/**
+ *  Asks the delegate for custom text for a date
+ *
+ *  @param controller the calendarView Controller
+ *  @param date       the date (Midnight GMT)
+ */
+- (nullable NSString *)simpleCalendarViewController:(PDTSimpleCalendarViewController *)controller textForDate:(NSDate *)date;
 
 @end;
+NS_ASSUME_NONNULL_END
diff --git a/PDTSimpleCalendar/PDTSimpleCalendarViewController.m b/PDTSimpleCalendar/PDTSimpleCalendarViewController.m
index 658e711..51565ee 100644
--- a/PDTSimpleCalendar/PDTSimpleCalendarViewController.m
+++ b/PDTSimpleCalendar/PDTSimpleCalendarViewController.m
@@ -172,7 +172,14 @@ - (NSDate *)lastDate
 
 - (void)setLastDate:(NSDate *)lastDate
 {
-    _lastDate = [self clampDate:lastDate toComponents:kCalendarUnitYMD];
+    NSDate *clampedDate = [self clampDate:lastDate toComponents:kCalendarUnitYMD];
+
+    if ([_lastDate compare: clampedDate] != NSOrderedSame) {
+
+        _lastDateMonth = nil;
+        [self.collectionViewLayout invalidateLayout];
+    }
+    _lastDate = clampedDate;
 }
 
 - (NSDate *)lastDateMonth
@@ -308,7 +315,7 @@ - (void)viewDidLoad
 
 #pragma mark - Rotation Handling
 
-- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration
+- (void) viewWillTransitionToSize: (CGSize) size withTransitionCoordinator: (id<UIViewControllerTransitionCoordinator>) coordinator
 {
     [self.collectionView.collectionViewLayout invalidateLayout];
 }
@@ -375,28 +382,36 @@ - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cell
     if (cellDateComponents.month == firstOfMonthsComponents.month) {
         isSelected = ([self isSelectedDate:cellDate] && (indexPath.section == [self sectionForDate:cellDate]));
         isToday = [self isTodayDate:cellDate];
-        [cell setDate:cellDate calendar:self.calendar];
+
+        //Ask the delegate if this date should have custom text.
+        if ([self.delegate respondsToSelector:@selector(simpleCalendarViewController:textForDate:)]) {
+            NSString * customText = [self.delegate simpleCalendarViewController:self textForDate:cellDate];
+            if (customText) {
+                [cell setText: customText];
+            }
+            else { [cell setDate:cellDate calendar:self.calendar]; }
+        }
+        else { [cell setDate:cellDate calendar:self.calendar]; }
+
+        //Ask the delegate if this date should have specific colors.
+        if ([self.delegate respondsToSelector:@selector(simpleCalendarViewController:textColorForDate:)]) {
+            cell.textDefaultColor = [self.delegate simpleCalendarViewController:self textColorForDate:cellDate];
+        }
 
         //Ask the delegate if this date should have specific colors.
         if ([self.delegate respondsToSelector:@selector(simpleCalendarViewController:shouldUseCustomColorsForDate:)]) {
             isCustomDate = [self.delegate simpleCalendarViewController:self shouldUseCustomColorsForDate:cellDate];
         }
 
-
     } else {
         [cell setDate:nil calendar:nil];
     }
-
-    if (isToday) {
-        [cell setIsToday:isToday];
-    }
-
-    if (isSelected) {
-        [cell setSelected:isSelected];
-    }
+    [cell setToday: isToday];
+    [cell setSelected: isSelected];
 
     //If the current Date is not enabled, or if the delegate explicitely specify custom colors
     if (![self isEnabledDate:cellDate] || isCustomDate) {
+        cell.textDefaultColor = cell.textDisabledColor;
         [cell refreshCellColors];
     }
 
@@ -444,8 +459,14 @@ - (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView
 
         return headerView;
     }
+    else {
 
-    return nil;
+        PDTSimpleCalendarViewHeader *headerView = [self.collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:PDTSimpleCalendarViewHeaderIdentifier forIndexPath:indexPath];
+
+        headerView.bounds = CGRectZero;
+
+        return headerView;
+    }
 }
 
 #pragma mark - UICollectionViewFlowLayoutDelegate
@@ -454,7 +475,8 @@ - (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollection
 {
     CGFloat itemWidth = floorf(CGRectGetWidth(self.collectionView.bounds) / self.daysPerWeek);
 
-    return CGSizeMake(itemWidth, itemWidth);
+    // Limit the height with wide displays.
+    return CGSizeMake(itemWidth, MIN(itemWidth, round(kPDTSimpleCalendarCircleSize * 1.2)));
 }
 
 #pragma mark - UIScrollViewDelegate
@@ -495,7 +517,6 @@ - (void)hideOverlayView
     }];
 }
 
-#pragma mark -
 #pragma mark - Calendar calculations
 
 - (NSDate *)clampDate:(NSDate *)date toComponents:(NSUInteger)unitFlags
@@ -619,7 +640,7 @@ - (UIColor *)simpleCalendarViewCell:(PDTSimpleCalendarViewCell *)cell circleColo
     }
 
     if ([self.delegate respondsToSelector:@selector(simpleCalendarViewController:circleColorForDate:)]) {
-        return [self.delegate simpleCalendarViewController:self circleColorForDate:date];
+        return [self.delegate simpleCalendarViewController:self circleColorForDate:date] ?: cell.circleDefaultColor;
     }
 
     return nil;
@@ -628,11 +649,11 @@ - (UIColor *)simpleCalendarViewCell:(PDTSimpleCalendarViewCell *)cell circleColo
 - (UIColor *)simpleCalendarViewCell:(PDTSimpleCalendarViewCell *)cell textColorForDate:(NSDate *)date
 {
     if (![self isEnabledDate:date]) {
-        return cell.textDisabledColor;
+        return cell.textDefaultColor;
     }
 
     if ([self.delegate respondsToSelector:@selector(simpleCalendarViewController:textColorForDate:)]) {
-        return [self.delegate simpleCalendarViewController:self textColorForDate:date];
+        return [self.delegate simpleCalendarViewController:self textColorForDate:date] ?: cell.textDefaultColor;
     }
 
     return nil;
diff --git a/PDTSimpleCalendar/PDTSimpleCalendarViewFlowLayout.h b/PDTSimpleCalendar/PDTSimpleCalendarViewFlowLayout.h
index 61a3c5b..98e36aa 100644
--- a/PDTSimpleCalendar/PDTSimpleCalendarViewFlowLayout.h
+++ b/PDTSimpleCalendar/PDTSimpleCalendarViewFlowLayout.h
@@ -6,7 +6,8 @@
 //  Copyright (c) 2013 Producteev. All rights reserved.
 //
 
-#import <UIKit/UIKit.h>
+@import UIKit;
+NS_ASSUME_NONNULL_BEGIN
 
 extern const CGFloat PDTSimpleCalendarFlowLayoutMinInterItemSpacing;
 extern const CGFloat PDTSimpleCalendarFlowLayoutMinLineSpacing;
@@ -19,3 +20,4 @@ extern const CGFloat PDTSimpleCalendarFlowLayoutHeaderHeight;
 @interface PDTSimpleCalendarViewFlowLayout : UICollectionViewFlowLayout
 
 @end
+NS_ASSUME_NONNULL_END
diff --git a/PDTSimpleCalendar/PDTSimpleCalendarViewHeader.h b/PDTSimpleCalendar/PDTSimpleCalendarViewHeader.h
index 377304b..ae4299b 100644
--- a/PDTSimpleCalendar/PDTSimpleCalendarViewHeader.h
+++ b/PDTSimpleCalendar/PDTSimpleCalendarViewHeader.h
@@ -6,12 +6,13 @@
 //  Copyright (c) 2013 Producteev. All rights reserved.
 //
 
-#import <UIKit/UIKit.h>
+@import UIKit;
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  The `PDTSimpleCalendarViewHeader` class displays the month name and year.
  */
-@interface PDTSimpleCalendarViewHeader : UICollectionReusableView
+@interface PDTSimpleCalendarViewHeader : UICollectionReusableView <UIAppearanceContainer>
 
 /**
  *  Label that display the month and year
@@ -36,3 +37,4 @@
 @property (nonatomic, strong) UIColor *separatorColor UI_APPEARANCE_SELECTOR;
 
 @end
+NS_ASSUME_NONNULL_END
diff --git a/PDTSimpleCalendar/PDTSimpleCalendarViewHeader.m b/PDTSimpleCalendar/PDTSimpleCalendarViewHeader.m
index 92bf498..c2484fb 100644
--- a/PDTSimpleCalendar/PDTSimpleCalendarViewHeader.m
+++ b/PDTSimpleCalendar/PDTSimpleCalendarViewHeader.m
@@ -8,31 +8,44 @@
 
 #import "PDTSimpleCalendarViewHeader.h"
 
-const CGFloat PDTSimpleCalendarHeaderTextSize = 12.0f;
+const CGFloat kPDTSimpleCalendarHeaderTextSize = 12.0f;
+
+@interface PDTSimpleCalendarViewHeader ()
+
+@property (nonatomic, nonnull, retain) UIView *separatorView;
+
+@end
 
 @implementation PDTSimpleCalendarViewHeader
 
-- (id)initWithFrame:(CGRect)frame
++ (void)initialize {
+    if (self == [PDTSimpleCalendarViewHeader class]) {
+        // Set the UIAppearance default values.
+        PDTSimpleCalendarViewHeader *proxy = [PDTSimpleCalendarViewHeader appearance];
+
+        [proxy setSeparatorColor: [UIColor lightGrayColor]];
+
+        [proxy setTextColor: [UIColor blackColor]];
+        [proxy setTextFont: [UIFont systemFontOfSize: kPDTSimpleCalendarHeaderTextSize]];
+    }
+}
+
+- (instancetype)initWithFrame:(CGRect)frame
 {
     self = [super initWithFrame:frame];
     if (self) {
         // Initialization code
         _titleLabel = [[UILabel alloc] init];
-        [_titleLabel setFont:self.textFont];
-        [_titleLabel setTextColor:self.textColor];
-        [_titleLabel setBackgroundColor:[UIColor clearColor]];
-
         [self addSubview:_titleLabel];
         [_titleLabel setTranslatesAutoresizingMaskIntoConstraints:NO];
 
-        UIView *separatorView = [[UIView alloc] init];
-        [separatorView setBackgroundColor:self.separatorColor];
-        [self addSubview:separatorView];
-        [separatorView setTranslatesAutoresizingMaskIntoConstraints:NO];
+        _separatorView = [[UIView alloc] init];
+        [self addSubview: _separatorView];
+        [_separatorView setTranslatesAutoresizingMaskIntoConstraints:NO];
 
         CGFloat onePixel = 1.0f / [UIScreen mainScreen].scale;
         NSDictionary *metricsDictionary = @{@"onePixel" : [NSNumber numberWithFloat:onePixel]};
-        NSDictionary *viewsDictionary = @{@"titleLabel" : self.titleLabel, @"separatorView" : separatorView};
+        NSDictionary *viewsDictionary = @{@"titleLabel" : _titleLabel, @"separatorView" : _separatorView};
 
         [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|-(==10)-[titleLabel]-(==10)-|" options:0 metrics:nil views:viewsDictionary]];
         [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[titleLabel]|" options:0 metrics:nil views:viewsDictionary]];
@@ -44,47 +57,19 @@ - (id)initWithFrame:(CGRect)frame
     return self;
 }
 
+- (void) didMoveToWindow {
 
-#pragma mark - Colors
-
-- (UIColor *)textColor
-{
-    if(_textColor == nil) {
-        _textColor = [[[self class] appearance] textColor];
-    }
-
-    if(_textColor != nil) {
-        return _textColor;
-    }
-
-    return [UIColor grayColor];
-}
-
-- (UIFont *)textFont
-{
-    if(_textFont == nil) {
-        _textFont = [[[self class] appearance] textFont];
-    }
-
-    if(_textFont != nil) {
-        return _textFont;
-    }
-
-    return [UIFont systemFontOfSize:PDTSimpleCalendarHeaderTextSize];
-}
+    [super didMoveToWindow];
 
-- (UIColor *)separatorColor
-{
-    if(_separatorColor == nil) {
-        _separatorColor = [[[self class] appearance] separatorColor];
-    }
+    if (self.window) {
+        // Use the UIAppearance properties only after they been finalized by being
+        // inserted into a live window.
+        self.separatorView.backgroundColor = self.separatorColor;
 
-    if(_separatorColor != nil) {
-        return _separatorColor;
+        self.titleLabel.font = self.textFont;
+        self.titleLabel.textColor = self.textColor;
+        self.titleLabel.backgroundColor = UIColor.clearColor;
     }
-
-    return [UIColor lightGrayColor];
 }
 
-
 @end
diff --git a/PDTSimpleCalendar/PDTSimpleCalendarViewWeekdayHeader.h b/PDTSimpleCalendar/PDTSimpleCalendarViewWeekdayHeader.h
index 03f832a..8679108 100644
--- a/PDTSimpleCalendar/PDTSimpleCalendarViewWeekdayHeader.h
+++ b/PDTSimpleCalendar/PDTSimpleCalendarViewWeekdayHeader.h
@@ -6,7 +6,8 @@
 //  Copyright (c) 2015 MorningCall. All rights reserved.
 //
 
-#import <UIKit/UIKit.h>
+@import UIKit;
+NS_ASSUME_NONNULL_BEGIN
 
 extern const CGFloat PDTSimpleCalendarWeekdayHeaderSize;
 extern const CGFloat PDTSimpleCalendarWeekdayHeaderHeight;
@@ -17,13 +18,13 @@ typedef NS_ENUM (NSInteger, PDTSimpleCalendarViewWeekdayTextType) {
     PDTSimpleCalendarViewWeekdayTextTypeStandAlone
 };
 
-@interface PDTSimpleCalendarViewWeekdayHeader : UIView
+@interface PDTSimpleCalendarViewWeekdayHeader : UIView <UIAppearanceContainer>
 
 /**
  *  Init with calendar
  *
  *  @param calendar the calendar used to generate the view.
- *  @param textType
+ *  @param textType The text style.
  */
 - (id)initWithCalendar:(NSCalendar *)calendar weekdayTextType:(PDTSimpleCalendarViewWeekdayTextType)textType;
 
@@ -43,3 +44,4 @@ typedef NS_ENUM (NSInteger, PDTSimpleCalendarViewWeekdayTextType) {
 @property (nonatomic, strong) UIColor *headerBackgroundColor UI_APPEARANCE_SELECTOR;
 
 @end
+NS_ASSUME_NONNULL_END
diff --git a/PDTSimpleCalendar/PDTSimpleCalendarViewWeekdayHeader.m b/PDTSimpleCalendar/PDTSimpleCalendarViewWeekdayHeader.m
index 2d1a4d4..22b508e 100644
--- a/PDTSimpleCalendar/PDTSimpleCalendarViewWeekdayHeader.m
+++ b/PDTSimpleCalendar/PDTSimpleCalendarViewWeekdayHeader.m
@@ -11,26 +11,40 @@
 const CGFloat PDTSimpleCalendarWeekdayHeaderSize = 12.0f;
 const CGFloat PDTSimpleCalendarWeekdayHeaderHeight = 20.0f;
 
+@interface PDTSimpleCalendarViewWeekdayHeader ()
+
+@property (nonatomic, retain) NSCalendar *calendar;
+@property (nonatomic) PDTSimpleCalendarViewWeekdayTextType weekdayTextType;
+@property (nonatomic, retain) NSArray *weekdaySymbols;
+
+@end
+
 @implementation PDTSimpleCalendarViewWeekdayHeader
 
-/*
-// Only override drawRect: if you perform custom drawing.
-// An empty implementation adversely affects performance during animation.
-- (void)drawRect:(CGRect)rect {
-    // Drawing code
++ (void)initialize {
+    // Set the UIAppearance default values.
+    if (self == [PDTSimpleCalendarViewWeekdayHeader class]) {
+        PDTSimpleCalendarViewWeekdayHeader *proxy = [PDTSimpleCalendarViewWeekdayHeader appearance];
+
+        [proxy setHeaderBackgroundColor: [UIColor whiteColor]];
+
+        [proxy setTextColor: [UIColor blackColor]];
+        [proxy setTextFont: [UIFont systemFontOfSize: PDTSimpleCalendarWeekdayHeaderSize]];
+    }
 }
-*/
 
 - (id)initWithCalendar:(NSCalendar *)calendar weekdayTextType:(PDTSimpleCalendarViewWeekdayTextType)textType
 {
     self = [super init];
     if (self)
     {
-        self.backgroundColor = self.headerBackgroundColor;
+        _calendar = calendar;
+        _weekdayTextType = textType;
+
         NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
         dateFormatter.calendar = calendar;
         NSArray *weekdaySymbols = nil;
-        
+
         switch (textType) {
             case PDTSimpleCalendarViewWeekdayTextTypeVeryShort:
                 weekdaySymbols = [dateFormatter veryShortWeekdaySymbols];
@@ -42,27 +56,37 @@ - (id)initWithCalendar:(NSCalendar *)calendar weekdayTextType:(PDTSimpleCalendar
                 weekdaySymbols = [dateFormatter standaloneWeekdaySymbols];
                 break;
         }
-        
-        NSMutableArray *adjustedSymbols = [NSMutableArray arrayWithArray:weekdaySymbols];
-        for (NSInteger index = 0; index < (1 - calendar.firstWeekday + weekdaySymbols.count); index++) {
+        _weekdaySymbols = weekdaySymbols;
+    }
+    return self;
+}
+
+- (void) didMoveToWindow {
+
+    [super didMoveToWindow];
+
+    if (self.window) {
+        // Use the UIAppearance properties only after they been finalized by being
+        // inserted into a live window.
+        self.backgroundColor = self.headerBackgroundColor;
+
+        NSMutableArray *adjustedSymbols = [NSMutableArray arrayWithArray: self.weekdaySymbols];
+        for (NSInteger index = 0; index < (1 - self.calendar.firstWeekday + self.weekdaySymbols.count); index++) {
             NSString *lastObject = [adjustedSymbols lastObject];
             [adjustedSymbols removeLastObject];
             [adjustedSymbols insertObject:lastObject atIndex:0];
         }
-        
         if (adjustedSymbols.count == 0) {
-            return self;
+            return;
         }
-        
         UILabel *firstWeekdaySymbolLabel = nil;
-        
         NSMutableArray *weekdaySymbolLabelNameArr = [NSMutableArray array];
         NSMutableDictionary *weekdaySymbolLabelDict = [NSMutableDictionary dictionary];
         for (NSInteger index = 0; index < adjustedSymbols.count; index++)
         {
             NSString *labelName = [NSString stringWithFormat:@"weekdaySymbolLabel%d", (int)index];
             [weekdaySymbolLabelNameArr addObject:labelName];
-            
+
             UILabel *weekdaySymbolLabel = [[UILabel alloc] init];
             weekdaySymbolLabel.font = self.textFont;
             weekdaySymbolLabel.text = [adjustedSymbols[index] uppercaseString];
@@ -70,64 +94,21 @@ - (id)initWithCalendar:(NSCalendar *)calendar weekdayTextType:(PDTSimpleCalendar
             weekdaySymbolLabel.textAlignment = NSTextAlignmentCenter;
             weekdaySymbolLabel.backgroundColor = [UIColor clearColor];
             weekdaySymbolLabel.translatesAutoresizingMaskIntoConstraints = NO;
-            
+
             [self addSubview:weekdaySymbolLabel];
-            
+
             [weekdaySymbolLabelDict setObject:weekdaySymbolLabel forKey:labelName];
             [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:[NSString stringWithFormat:@"V:|[%@]|", labelName] options:0 metrics:nil views:weekdaySymbolLabelDict]];
-            
+
             if (firstWeekdaySymbolLabel == nil) {
                 firstWeekdaySymbolLabel = weekdaySymbolLabel;
             } else {
                 [self addConstraint:[NSLayoutConstraint constraintWithItem:weekdaySymbolLabel attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:firstWeekdaySymbolLabel attribute:NSLayoutAttributeWidth multiplier:1 constant:0]];
             }
         }
-        
         NSString *layoutString = [NSString stringWithFormat:@"|[%@(>=0)]|", [weekdaySymbolLabelNameArr componentsJoinedByString:@"]["]];
         [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:layoutString options:NSLayoutFormatAlignAllCenterY metrics:nil views:weekdaySymbolLabelDict]];
-
-    }
-    
-    return self;
-}
-
-- (UIColor *)textColor
-{
-    if(_textColor == nil) {
-        _textColor = [[[self class] appearance] textColor];
-    }
-    
-    if(_textColor != nil) {
-        return _textColor;
-    }
-    
-    return [UIColor blackColor];
-}
-
-- (UIFont *)textFont
-{
-    if(_textFont == nil) {
-        _textFont = [[[self class] appearance] textFont];
-    }
-    
-    if(_textFont != nil) {
-        return _textFont;
-    }
-    
-    return [UIFont systemFontOfSize:PDTSimpleCalendarWeekdayHeaderSize];
-}
-
-- (UIColor *)headerBackgroundColor
-{
-    if(_headerBackgroundColor == nil) {
-        _headerBackgroundColor = [[[self class] appearance] headerBackgroundColor];
-    }
-    
-    if(_headerBackgroundColor != nil) {
-        return _headerBackgroundColor;
     }
-    
-    return [UIColor whiteColor];
 }
 
 @end