The size of the chat message composition area in the bottom of the chat room is too small by default, and it doesn't shrink when the page gets too small. Both problems are easily solvable.
Current Default Width
The current default is 540 pixels. Here is a picture of a message one character shy of the limit. It's too small to hold what it was created for.
Proposed Default Width
Make it 820 pixels. This is the smallest width that holds the maximum message length without clipping. On a 1920 by 1080 monitor, this still leaves half of the entire bar unused.
Add a Maximum Width
As the page shrinks, the entire page adjusts, but the chat box stands strong! It floats off into nothingness, and your message gets clipped. Add a maximum width that shrinks with the page. Add a minimum width that keeps it from shrinking into ugliness.