docs: function supportsCssVariables(forceRefresh = false) {
    if (typeof supportsCssVariables_ === 'boolean' && !forceRefresh) {
      return supportsCssVariables_;
    }
  
    const supportsFunctionPresent =
      win.CSS && typeof win.CSS.supports === 'function';
    if (!supportsFunctionPresent) {
      return;
    }
  
    const explicitlySupportsCssVars = win.CSS.supports('--css-vars', 'yes');
    /*
     * See: https://bugs.webkit.org/show_bug.cgi?id=154669
     * See: README section on Safari
     */
    const weAreFeatureDetectingSafari10plus =
      win.CSS.supports('(--css-vars: yes)') &&
      win.CSS.supports('color', '#00000000');
  
    if (explicitlySupportsCssVars || weAreFeatureDetectingSafari10plus) {
      supportsCssVariables_ = !detectEdgePseudoVarBug();
    } else {
      supportsCssVariables_ = false;
    }
    return supportsCssVariables_;
  }