Primer tagline increase font size

I’ve poured over every line of the style.css and cannot find the place where I can increase the tagline under my blog title in the header image section. While I thought it would be the following code, nothing that I do to change that with font-size: xxpx; makes any difference in the size of the tagline. Thanks in advance for the help!

.site-description {
  font-size: 34px;
  color: #ffffff; }

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