Table backgrounds dont span full width anymore

**Link to problem area**: https://spec.matrix.org/v1.17/client-server-api/#get_matrixclientv3adminwhoisuserid

**Issue**

The box goes further than the table again. Iirc that was fixed in the past so it is likely a regression.
It seems to also not affect all tables but only some (Maybe the others push it far enough?)

Start at the linked /v1.17/client-server-api/#get_matrixclientv3adminwhoisuserid section and inspect the table markup and styling around the affected example. Compare it with tables whose backgrounds span correctly; done means the surrounding box and table background align consistently, including for tables that do not already force the full width.

Written by the indexing model from the issue text.