Marker tooltip/popup text gets clipped at the top for Style metadata

[bgrins]

STR:

• Open https://perfht.ml/2RF2Qtl
• Hover the style marker

I can see just the bottom of "Styles reused" metadata, but there's more interesting stuff above about the number of elements traversed / matched / etc. If the tooltip doesn't have enough space I'd rather see the top of it and have the bottom stack portion get clipped.

[gregtatum]

Duplicate of #883. I included the STR in that issue as well, since it's a nice one.