Hey @kcn!
We don't unfortunately have options for this on the Themes tab right now, so the only way to do that would be through theme customization. If you're familiar with HTML and CSS you can do that by going to the Themes tab and clicking on "Edit HTML / CSS".
You can also suggest that on our Vote on Features board if you'd like us to add options like that:
https://community.weebly.com/t5/Vote-on-Features/idb-p/IdeaExchange
