Large font sizes break the appearance of the preset sizes dropdown

[kjellr]

Describe the bug

If a theme provides very large font sizes as presets, it breaks the appearance of the preset size dropdown.

To reproduce
Steps to reproduce the behavior:

1. Use a theme that provides a large font size (96, for example).
2. Use the preset sizes dropdown.
3. Notice the overflow.

Expected behavior

Font size representations there should be capped to a size that prevents them from overflowing their container.

Screenshots

Gutenberg 9.1.0
Discovered while building the Twenty Twenty One Theme.

[aristath]

Ideally I'd say they shouldn't even have a preview... a simple drop down with the labels would work fine and won't break if the font sizes are not defined in pixels (I actually came across this while building an FSE theme).
Everything breaks if the font-size is something like a calc() containing a css var

[kjellr]

A couple quick ideas:

At the very least, we can set overflow-y to hidden on these fields. That'll improve the appearance somewhat:

Alternatively, when we set the inline value, instead of setting the value directly, we could use something like min(32px, [actual value]). to ensure that even if the value is huge, it'll max out at a reasonable size: