Flex overflow + Webkit

Webkit has a bug (I think?) that doesn't let `overflow: hidden` and `overflow: scroll` work nicely together when used by a flex box. This could possibly be a mistake on my part when structuring the flex boxes but a workaround or fix is needed.

**Browsers Effected**
- Webkit based browsers, e.g. Safari

**Pages Effected**
- /messages/{id}

The previous messages cannot be scrolled through on the sidebar.

**In other words:** the messages UI does not work properly on Safari.