The SyntaxHighlighter Evolved plugin is great, but there is no way to adjust the font size! Here is what worked for me.
![](https://i0.wp.com/terheyden.com/wp-content/uploads/2021/05/2021-05-14_21-33-39-syn1-1.png?resize=325%2C307&ssl=1)
From your WordPress admin panel, open Appearance » Customize.
![](https://i0.wp.com/terheyden.com/wp-content/uploads/2021/05/2021-05-14_21-35-13-syn2.png?resize=317%2C151&ssl=1)
Then, on the Customize page, click on Additional CSS.
![](https://i0.wp.com/terheyden.com/wp-content/uploads/2021/05/2021-05-14_21-36-21-syn3.png?resize=287%2C190&ssl=1)
In the little Additional CSS box we’re going to restyle SyntaxHighlighter and make the font size 75% of our normal blog font size (set the percentage to whatever works for you, of course).
div.wp-block-syntaxhighlighter-code {
font-size: 75% !important;
}
Be sure to click Publish, and you’re done!