web/style: Only add bottom border when requested to <th>'s in <tbody>

When the <th> is a row heading, the border looks as ugly as heck.

Add a special case for <th> in <tbody> as a long heading.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
web/style: Remove ugly white border around tables on mobile devices

Signed-off-by: Timothy Gu <timothygu99@gmail.com>