Invert light images in dark themes

CSS `filter: invert(1.0)` can be easily applied to almost every image when a dark theme is selected. The result is very nice and will allow us to not rewrite/redesign every image for the dark themes.

However, we need a "not-invert" class for the images for which this effect doesn't work very well or the "themed" SVG already pointing to the CSS variables of the selected theme.

The issue does not name a file or test. Start by locating the dark-theme styles and the image markup, then verify how CSS filter: invert(1.0) is applied. Done means dark themes invert suitable images while images marked not-invert and themed SVGs remain unchanged.

Written by the indexing model from the issue text.