User Agent is: Mozilla/5.0 (Linux; Android 8.1.0; ULTRA Build/OPM2.171019.012) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.126 Mobile Safari/537.36.
You’re mixing up HTML and CSS, you’ve put an HTML tag into CSS which isn’t valid, they’re completely different languages. You can write CSS inside a <style> tag in HTML. But the line I’ve quoted is HTML, it goes in the HTML
Vertically or horizontally? Or both? In what context (ie what does the HTML look like, what does the CSS look like, what exactly are you trying to achieve, style-wise)?
You need to try I’m afraid, do you have an example from somewhere that describes visually what you mean? Centring things horizontally is trivial (text-align: center will do it), but it might not work for what you want to do, there are multiple ways to do it that may be more appropriate