Fix Safari rendering problem for font elements that reach beyond vertical metrics limits

[kontur]

Very much an edge case, but Safari seems to not properly update font rendering for fonts that have elements beyond their vertical metrics.

I've attempted backface-visibility / translateZ(0) hacks to force the repaint, and that updates the beyond-the-box elements, but doing so after each keystroke seems excessive.

This might also be a wontfix issue with a documentation entry encouraging users to set more appropriate vertical metrics.