Code blocks can't be rendered in tabs

[montanalow]

The markdown for !!! codeblock support doesn't work inside a tab, so these (and all other ``` codeblocks) look naked without the white border. White border should be standard css for all ``` codeblocks, not just !!! codeblocks.

Ideally, we'd just have a single syntax too, like ```sql time="123.45 ms"