The Cell Border section in the new Calc sidebar is a step in the right direction. Using it, I can now easily create a table with thin framed cells inside and a thick frame outside - which was nearly impossible earlier (or, at least, I did not find out how to do that).
However, the default thick frames are too thick.
The unnamed dropdown menu there offers four frame thicknesses: 0.05pt, 2.5pt, 4pt and 5pt. The thick frame in the menu on the left seems to be coupled with this and has thickness 2.5pt - which is too thick. Therefore, I recommend to change the scale to 0.05pt, 1pt, 2pt and 3pt, since then the thicker frame in the Cell Border dropdown menu will be 1pt - which is the same, as MS Office uses the same dimensions. In that case LO will be compatible and, as I think, many users will appreciate it.
Frames in LO have also other problems, but correction of this one (perhaps not that complicated), would improve usability significantly.
You should try the master in which Kohei Yoshida did a great job on cell border recently (see his blog).
Set as enhancement.
Best regards. JBF
Hi Milos, which menu do you mean exactly? Is this still reproducable in 5.2?
Created attachment 127355 [details]
screenshot showing currently predefined cell borders
It is the "Select the line style of the borders". A screenshot is attached
Default widths have been reworked in bug 48622 / https://git.libreoffice.org/core/commit/41b99644e8913dd4797775f4931382e93fa12a00 .
Closing this now. If any further fixes are needed, please open a new specific bug report.