You can't, you're using OnDemand, which means you can't hack the underlying CSS.
If you've got your own installation, you'd be able to fiddle with the css in there. If your improvements really make it less ugly, it would be nice to share it with Atlassian to see if they'd incorporate any of your prettying.
The Jira Marketing team is putting together an ebook on migrating to Data Center. We're looking for pro tips on how you staffed your project team and organized your Proof of Concept. Share yo...
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG
You're one step closer to meeting fellow Atlassian users at your local meet up. Learn more about AUGs