[ticket/10472] Fix ACP overflow:hidden problems for medium-sized screens

https://tracker.phpbb.com/browse/PHPBB3-10472

Hope to fix a long standing problem. Certain tables in the ACP are particularly wide (like add/edit smilies), and with an `overflow: hidden` rule they are simply not visible at all.

By reducing the width of some of the worst offenders (`input[type="number"]`) in particular, and having proper clearing rules, we can show these tables, even though they break out of the container.

I know its not ideal, but having some horizontal scrolling outside of the container is significantly better than not being able to see certain settings at all.

PHPBB3-10472
I actually don't know. It's been so long since I made this. I probably needed a stronger selector somewhere. But I can't find it anymore.

Also, since the padding problem is mostly related to Firefox, I think I'm going to change the padding to `-moz-padding-end` https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-padding-end