Customizer Theme Installer version and description should not be floated

[afercia]

Small layout bug noticed while testing the Customizer. See in the screenshot below: the Theme Installer when the Theme description is very short.

Not sure why the version and description are floated in the first place, maybe they shouldn't.

[mehulkaklotar]

theme-description class should have width : 100% instead of max-width

[obenland]

In 33651:

Themes: Prevent short descriptions from wrapping version info.

Props mehulkaklotar for initial patch.
Fixes #33248.