8a7771ba42
For a variety of reasons (see bug 1933080 and bug 1508388), the new tab page needs to fake a caret. This will allow them to fake it more reliably. I thought of just exposing this to CSS via an env() var, but turning the negatives into something usable generically seems a bit hard (e.g. one should be calc(inf) or so, and the other should somehow not animate at all, which is not trivial to express on a single value. Differential Revision: https://phabricator.services.mozilla.com/D236676