Please can you make the Code Panel full-width too.
Using Firefox's Inspector, the <div> that needs altering is:

<div data-selector="repos-split-pane-content" tabindex="0" class="Box-sc-g0xbh4-0 jgEDtJ">

It has the property:

max-width: 1012px;

Turning that off improves the look:

Before

After

That probably means that we need, either/or:

width: 100% !important;
max-width: none !important;

Thanks ❤️