Custom styling to fix some visual issues with the wiki.

[KaiDevvy]

Jekyll-rtd supports adding custom styling through a particular include file.

In this change:

• the visual appearance of toast cards is changed to be less intrusive.
• The wasted empty space on the right side of the page is removed.

You can see how this change looks visually in the before and after screenshots below, or see a live preview here.

Page Viewport | Before

Page Viewport | After

Toast cards | Before

Toast cards | After