Description:
When using another theme than deffault, such as the Dark theme, in LibreOffice and using LibreOffice Calc or Writer maximized to thew extents of a wide screen monitor, the theme colour does not reach all the way to the left and right borders of the ribbon bar. 

Steps to Reproduce:
1. Use LibreOffice on an ultrawide monitor with a resolution of 3440 * 1440 pixels
2. Change the theme to Dark theme
3. Maximize the LibreOffice to the extents of the ultrawide screen

Actual Results:
The theme colour in the ribbon is rendered in the middle only.

Expected Results:
It should have rendered the theme colour all the way from the left border to the right border covering a 100% width of the screen.


Reproducible: Always


User Profile Reset: Yes

Additional Info:
I did actually *not* reset my profile as required in the step below, as that seemed far too complicated.