`center` is a [deprecated html tag](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/center). I'm guessing you're using it because it's already used in the vis header. Since it's only used in those two places, I think it's worth fixing. It looks like they both only contain inline elements, so you should be able to just change it to a div and add `text-align:center;`