Release 0.43 UI Polish + Fixes

* Fixed Live Preview tooltip styling.
* Removed "Working Files" text-shadow because it's a label.
* Made it so that "Working Files" label doesn't show through when Working Files Settings icon is on top of it.
* Applied the right highlight value for dark primary buttons.
* Dropdown triangles should look like equilateral triangles like the rest of the triangles.
* Tweaked File Type Switcher triangle spacing and dimmed the triangle colors slightly to improve visual hierarchy.
* Added no-editor background image for dark UI.
* Added 3px spacing between "Update" and "Remove" button in Extension Manager.
* Tweaked quiet text color. It's not supposed to be the same as the ones in light UI.
* Made the extension manager info text quieter to break the UI up a bit.
* Made Dark spinner more saturated.
* Fix for #8817.
* Removed "bevels" on selection bar.
* Removed dark styles from side bar as dark styles aren't needed there.
* Fix for #8808.