Change border style (not color) of selected calc cell?

Hi,
somewhen between LO 25.x and 26.2.5.1 (Linux( the style of the border of a selected cell changed so that is now looking a little weird:
lo

Strange enough, the border reverts to the old style when selecting more than one call (although 26 has a new ugly white padding inside).

Is there any way to change the border back to 2px on all sides? Maybe via gtk.css of a theme?

Many thanks!
Frankl