R1:e59702569f8e

CSS adjustments to Conpherence

Summary:
**Fix Conpherence messages overlapping header in mobile mode**

Before:
{F413544}
After:
{F413546}

**Make Conpherence input box be one line even in desktop mode**

Before:
{F413541}
After:
{F413540}

This second change, in particular, is motivated by the fact that pressing `Enter` sends the message, whereas the multi-line box gives the impression that the `Enter` key would simply introduce a line break in the message. (That's still possible via `Shift`+`Enter`, btw.