Split from bug 166588 Appearance: the two colums are not aligned. The entire dialog looks rather unorganized. Instead of the current somewhat convoluted interface, just showing three Theme options: Light, Dark, System with a radio button would make a much nicer UI. A screenshot of how musicpod app presents its theme selection is attached. May I suggest to just call that headline "Theme" instead of "LibreOffice Themes". Users are very aware that they just opened LibreOffice app. See attachment 200825 [details]
I think this entry can fit here as well: use a similar approach for Customizations. The current UI is a great way to raise user frustration. Not everybody is an arch user and enjoys tinkering with complex settings.
Appearance panel on the Welcome dialog follows the layout of the Tools -> Options -> Appearance panel. No reason to try to reimplement for minimal visual improvement especially as the Appearance theme handling is currently being refactored for 25.8 It is no different than handling as for the User Interface panel which reuses the 'User Interface...' dialog layout. Simple code reuse, no reason to reimplement. -1
Appearance options panel being refactored as in bug 164970, final results there would control changes here.
Not related to the Welcome dialog. Sahil is busy working on this tab.