LessCSS 4.0 began to require parenthesis around division by default, in

order to force immediate evaluation. This change was made because CSS

now uses / as non-math syntax for a lot of modern rules. LessCSS

previously allowed codebases to opt into a parens-division mode that

played nicer with modern CSS, but with 4.0 they made that mode the

default.
We were already using parens around most of our division, but there were

a couple cases that produced outright errors, and some that likely were

now outputting bad CSS.
This change adds parens around all division remaining in our codebase.

Successfully compiled the CSS.
Went through the UI. Didn't see any obvious breakages, but we'll need

to test more as we move this to production.