feat: Minor visual tweaks

[Hanziness]

This PR includes some minor UI improvements:

• the settings panel's close button (and all text buttons) now uses the primary colour as its ring
• in dark mode, the settings panel now has an outline to help find its borders
• the upcoming schedule items are a bit more transparent and scaled down, the active item's ring should look better
• the schedule bar also has a thin outline in dark mode
• the to-do list's button is now tonal, resulting in proper contrast when activated
• the to-do list's close button now uses the primary colour scheme