Bright-colored icons (to investigate, not important)

[bethac07]

Right now, all of our icons are black, which in dark mode Piximi puts a little white box behind to make visible. If it's possible to just have them all a consistent bright color (like Piximi-logo-teal) that might be nice!

[bethac07]

To add clarification - you can make the icons any color you want here, I'm just not sure how jupyter book handles the behavior, if it just always makes squares behind the icons in dark mode, if it's doing something clever with looking at the color, etc.