Higher contrast font colors, more font size choices
Have the font color selection include fonts with better contrast levels from the background. On the standard white background (don't know about others as my company has disabled themes), colors other than black are extremely hard to read.
As other users have noted, please add more font size choices, particularly for Wiki page titles. They are barely distinguishable from subheadings.
Jean-Louis Beaulne commented
When switching from the Default (White) theme to the Dark or HighContrast themes, the font colors have better contrast so are more useful.
However, I prefer working with the White background so the colors don't offer the visual "pop" I am looking for.
If it's a matter of contrast, the color pallet could be translated when switching themes, so that, depending on the background colors, the font colors always provide good contrast.
Example: The green font color is a light green which doesn't contrast well with white background. In any theme that has dark background, keep that color ID as light green, and for light backgrounds (like white), make that color ID into a dark green that provides better contrast.
Thanks for the proposition.