There are multiple ways to adjust the CSS. I use the Dark theme as a base and my own on-site CSS regarding code is here.:

.codeblock { max-height: 37em; max-width: 72em; overflow: auto; margin
+-bottom: 10px; border: 1px dotted white; border-left: none; padding: 
+15px; }

pre { max-height: 42em; max-width: 75em; overflow: auto;  padding: 5px
+; }
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