Enhancement: Custom site colour theme

[ngjunsiang]

The page looks very much like a "default-theme" page. To better align it with the college website and open house theme, give the site a custom colour scheme that makes it more harmonious with those pages.

Task

1. Add a custom css file for the site to override default selectors
2. Link the css file appropriately in the templates
3. Build the site including the css file successfully

Deliverables

• The page uses the main college colours tastefully: red, blue, yellow
  • see https://www.nanyangjc.moe.edu.sg/ for an example of the colours used; need not follow exact colours, can use a colour wheel or theme helpers to select appropriate colours
• a css file (may need to be placed in a separate folder, e.g. static, otherwise place in main folder) is added to the repository, and editing it allows the site theming to be adjusted