Needed some level of harcoding though due to callouts using colors,
which can't be css colors as DOMPDF won't understand these.
Use css variables elsewhere and added new dark variants to fit a bit
better.
Due to causing content images to be rendered in unexpected ways.
- Also removed CSS filters from other image usage.
- Tweaked header CSS filtering to not be so aggressive.
- Forced WYSIWYG editor to be on its own layer since that would allow
massive larger performance increases in Safari, especially when using
dark mode.
Closes#2045.
Closes#2154.
- Updated editor, and other area, styles to look okay in dark mode.
- Used tinyMCE theme generator to create dark mode theme.
- Updated tinymce to latest 4x version.
- Most elements done, but still need to do editors, tables and final
pass.
- Toggled only by quick js check at the moment, checking via css media
query. Need to make into user-preference toggle.
For #1234
