Schedule View Fix

[miles-grant-ibigroup]

Description:
Thanks to the recently exposed CSS variables, the schedule viewer is now much more easily able to blend in to its surroundings!

PR Checklist:

• Does the code follow accessibility standards (WCAG 2.1 AA Compliant)?
• Are all languages supported (Internationalization/Localization)?
• Are appropriate Typescript types implemented?

[binh-dam-ibigroup]

For info, to use this PR, the CSS needs to include a declaration such as:

:root {
  --main-base-color: #084c8d;
  --main-accent-color: #eee;
}