Tree: leaf items have extra left padding causing icon misalignment with folders

[jerrythomas]

Problem

In the Tree component, leaf items (nodes without children) appear to have additional left padding compared to their parent folder/group items. This causes the leaf icons to be visually misaligned with the folder icons above them.

Steps to reproduce

1. Navigate to /playground/themes/components or /playground/components/tree
2. Expand a folder node
3. Observe that the leaf item icons are indented further right than the folder icons at the same nesting level

Expected

Leaf item icons should align horizontally with sibling folder icons at the same nesting level.

Affected

All themes — likely a base layout CSS issue rather than theme-specific.