This updates our old box elements for dark mode. This mainly just uses

Ink container and header styling.
We do have a couple of "special" box classes.
important, namely, is still used, but deprecated and should be

replaced with ink-c-alert. In the meantime, it's been styled to no

longer use the ancient icon we used to use (which feels very out of

place in the UI) and instead use the same icon that warning alerts use.
tip hasn't been used in ages, and has been removed.

Tested these boxes in both light and dark modes. The light and dark

mode boxes all looked correct.