Color scheme toolbar button does not apply to code samples

// ==UserScript==
// @name         Nushell.sh readable code blocks (LLM-generated)
// @namespace    Violentmonkey Scripts
// @version      1.0.0
// @description  Force Nushell docs code blocks to use black text on white background
// @match        https://www.nushell.sh/*
// @grant        none
// ==/UserScript==

(function () {
  'use strict';

  const STYLE_ID = 'vm-nushell-readable-code-blocks';

  function addStyle() {
    if (document.getElementById(STYLE_ID)) return;

    const style = document.createElement('style');
    style.id = STYLE_ID;
    style.textContent = `
      /* Target Shiki blocks on nushell.sh */
      div[data-highlighter="shiki"],
      div[data-highlighter="shiki"] pre.shiki,
      div[data-highlighter="shiki"] code,
      div[data-highlighter="shiki"] span {
        color: #000 !important;
        background: #fff !important;
      }

      /* Override Shiki CSS variables used by theme switchers */
      div[data-highlighter="shiki"] {
        --shiki-light: #000 !important;
        --shiki-dark: #000 !important;
        --shiki-onedarkpro: #000 !important;
        --shiki-light-bg: #fff !important;
        --shiki-dark-bg: #fff !important;
        --shiki-onedarkpro-bg: #fff !important;
      }

      div[data-highlighter="shiki"] pre.shiki {
        border: 1px solid #ddd !important;
        border-radius: 6px !important;
      }
    `;
    document.head.appendChild(style);
  }

  function fixInlineStyles(root = document) {
    const blocks = root.querySelectorAll('div[data-highlighter="shiki"]');
    for (const block of blocks) {
      block.style.setProperty('--shiki-light', '#000', 'important');
      block.style.setProperty('--shiki-dark', '#000', 'important');
      block.style.setProperty('--shiki-onedarkpro', '#000', 'important');
      block.style.setProperty('--shiki-light-bg', '#fff', 'important');
      block.style.setProperty('--shiki-dark-bg', '#fff', 'important');
      block.style.setProperty('--shiki-onedarkpro-bg', '#fff', 'important');

      const pre = block.querySelector('pre.shiki');
      if (pre) {
        pre.style.setProperty('color', '#000', 'important');
        pre.style.setProperty('background', '#fff', 'important');
      }

      const nodes = block.querySelectorAll('code, span');
      for (const node of nodes) {
        node.style.setProperty('color', '#000', 'important');
        node.style.setProperty('background', '#fff', 'important');
      }
    }
  }

  function init() {
    addStyle();
    fixInlineStyles();

    const observer = new MutationObserver((mutations) => {
      for (const mutation of mutations) {
        for (const node of mutation.addedNodes) {
          if (node.nodeType === 1) {
            fixInlineStyles(node);
          }
        }
      }
    });

    observer.observe(document.documentElement, {
      childList: true,
      subtree: true,
    });
  }

  if (document.readyState === 'loading') {
    document.addEventListener('DOMContentLoaded', init, { once: true });
  } else {
    init();
  }
})();