In before fox bans you
In all seriousness, please upgrade your install, 1.13 is a couple years out of date. You'll have to move over to using git to get the latest version. Suggest you re-read the Wiki to find the new details.
We are currently on Tiny Tiny RSS v17.1 (f45a115) - I might be 1 or 2 out of date thou
2nd, post your full platform, not just the TTRSS version, such as OS, webserver, PHP version, SQL version, etc.
Otherwise you might get a couple weeks ban from fox.
Also read the sticky about themes, you might have to update yours slightly to get it to work with the latest version.
After that, what might help you is playing with the dev console in whatever browser you are using, can help you find the correct element name of what you want to modify.
I don't have specifics or instructions on that for you, but should get you started, just start poking around in Google and see how you go.