Twenty Seventeen Theme Adding a Box/banner around/behind site title

The website is http://www.theloudsoul.com/ I am wondering if it is possible to create a banner or box around the site title? I found some CSS code that sort of worked, but it wasn’t the same color no matter what I tried, plus it made the site look funny because it was just a thick banner. I am trying to make my site title and description more readable. Would it be possible to also make the text on both a bit bigger? Any help would be greatly appreciated! Sorry if I did something wrong in new.