darkSnap/script.user.js

// ==UserScript==
// @name        DarkSnap
// @namespace   http://tampermonkey.net/
// @match       https://snap.berkeley.edu/*
// @exclude     *://snap.berkeley.edu/snap/*
// @grant       none
// @version     3
// @author      Swee
// @description Fork of https://forum.snap.berkeley.edu/t/18272
// @run-at      document-idle
// ==/UserScript==
//

if (document.querySelectorAll('[data-bs-theme]').length > 0) {
    // Set the data-bs-theme attribute to "dark"
    // By doing some inspectation I determined a lot of pages use
    // bootstrap 5, and this is how you make bootstrap go in dark mode
    document.documentElement.setAttribute('data-bs-theme', 'dark');
    document.documentElement.classList.add("text-white"); // Make the text white with a class, rather than custom CSS.
    console.info("This page uses BS5.")
} else {
    // Dark mode patches for non-bootstrap pages
    const noBoostrapStyle = document.createElement('style');
    noBoostrapStyle.innerHTML = `
      body {
        background: #212529;
        color: white;
      }
      .notes {
        background: #2D3142 !important;
      }
      .trapezoid {
        color: #2D3142;
      }
      .trapezoid-footer {
        color: #212529;
      }
    `;
    document.head.appendChild(noBoostrapStyle);
    console.info("This page does NOT use BS5.")
}
document.head.appendChild(style);