Height of Code Block

pre.wp-block-code.copy-the-code-target.language-cpp {
    max-height: 50vh;
}

“vh” is the height of the viewport. You may want to play around with the value, but 50% seems pretty good to me.

To add or override CSS: use the “Additional CSS” option in the customizer.? https://codex.www.ads-software.com/CSS#Custom_CSS_in_WordPress

Learn to use the Chrome Developer Tools or Firefox Developer Tools to help you see and test changes to your CSS.

Thank you Steve

Worked like a charm.