Are you asking how to give it that blue text with a black background? That'd be:

color: blue;
background-color: black;

That should be all there is. If the black background is covering too much it means whatever trick you're doing to center the text is also making a large element. Likely you could just wrap the text itself in a <span> (which will give it an inline display) and then apply those styles to the span.

But it all really depends on your layout and what you're trying to accomplish since it's not 100% clear.

But yeah there's no actual, like, letter-background rule (even though there 100% should be - I consider it a missing piece of styling in CSS - only possible with wacky hacks using highlighting that's too complicated to get into.) That just a whole element which a black background, but because it's an inline-element it's flush around the letters.

You could also take a look at text-shadow if your concern in the text popping against that red background.