When using this with BS3 the month popup size is computed smaller than when not.

That is because rem units are used, so the date picker is sized relative to the root font size. Default for browsers are typically 16px, bootstrap uses 10px. So adding this
html {font-size: 16px;}
fixes it. May fuck up other things on your site though...
See also #624
Thanks, it worked! I looked everywhere for the place in the code where the size is computed. But I didn't find it yet. Where is it?
It is not computed, just set with rem units in the style sheet. Not ideal, as pr discussion in #624
Most helpful comment
That is because rem units are used, so the date picker is sized relative to the root font size. Default for browsers are typically 16px, bootstrap uses 10px. So adding this
html {font-size: 16px;}fixes it. May fuck up other things on your site though...