Fix dark mode MR page sourcegraph conflicts

What does this MR do and why?

Fix bug introduced by !105041 (merged)

Screenshots

Before	After

How to set up and validate locally

snippet to apply changes to MR page:

var style = document.createElement('style');
style.innerText = `body.gl-dark {
  color-scheme: dark;
  --gray-10: #1f1e24;
  --border-color: #434248;
  --white: #333238;
  --black: #fff;
}`
document.head.appendChild(style);

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.