[grid] dividing line not visible in stacked inverted grid

[hugopeek]

Bug Report

When displaying an inverted divided grid on a dark background, the border-top of the column that should show the dividing line does not have enough specificity (when stacked).

Testcase

https://jsfiddle.net/bo3ht7mu/

Uncommenting the border-top rule with !important solves it. Also, moving that rule higher up seems to work.

Screenshot (if possible)

Version

2.9.3

[ko2in]

Fixed by #2924