>>/20810/
> custom.css is the customized thing for each board that resides in database or somewhere like this, so they serve it with specific code.

Yea, but I think it's just an oversight. There's already code in place for storing and serving compressed data out of the database but it's not used for the custom.css. I looked quickly at the upstream version and it doesn't seem like this bug is fixed there either
 >>/20811/
So it's not 1MB then? All the better
> ~250 requests <1kb each

> 1 second delay

> do not ddos poor imgur

that's a bit of an exaggeration

 >>/20813/
 >>/20818/
That clipping there is caused by the
divMessage { display: inline-block; }
You can try overriding it: 
divMessage { display: initial !important; }