STR:
  - Go to https://mozilla.github.io/pdf.js/web/viewer.html
  - Click on "Open File" and open a pdf

The `Download` button and the `Current view` one just disappear.
I can reproduce this bug with Firefox nightly, Chrome stable and Epiphany on debian.
? "-moz-toolbar-prefers-color-scheme"
          : "prefers-color-scheme";
      const mediaRule = `(${mediaMatcher}: dark)`;
      const mediaRegex = new RegExp(
        `^@media \\(${mediaMatcher}: dark\\) {\\n\\s*([\\w\\s-.,:;/\\\\{}()]+)\\n}$`
      );
      for (let i = 0, ii = cssRules.length; i < ii; i++) {
        const rule = cssRules[i];
        if (rule instanceof CSSMediaRule && rule.media?.[0] === mediaRule) {
          if (cssTheme === ViewerCssTheme.LIGHT) {
            styleSheet.deleteRule(i);
            return;
          }
          
          const darkRules = mediaRegex.exec(rule.cssText);
          if (darkRules?.[1]) {
            styleSheet.deleteRule(i);
            styleSheet.insertRule(darkRules[1], i);
          }
          return;
        }
      }
    } catch (reason) {
      console.error(`_forceCssTheme: "${reason?.message}".`);
    }
  },
  /**
   * @private
   */
  async _initializeViewerComponents() {