Blame for static/theme.js

// Run before the stylesheet so a saved theme is applied before the first paint.
(() => {
  const key = 'huggingpolls-theme';
  const system = window.matchMedia('(prefers-color-scheme: dark)');
  const valid = value => ['system', 'light', 'dark'].includes(value);
  let preference = 'system';
  try {
    const saved = localStorage.getItem(key);
    if (valid(saved)) preference = saved;
  } catch { /* The system theme still works when browser storage is blocked. */ }

  function apply() {
    const theme = preference === 'system' ? (system.matches ? 'dark' : 'light') : preference;
    document.documentElement.dataset.theme = theme;
    document.querySelector('meta[name="theme-color"]').content = theme === 'dark' ? '#11151d' : '#ffffff';
    const select = document.querySelector('#theme-select');
    if (select) select.value = preference;
    const status = document.querySelector('#theme-status');
    if (status) status.textContent = `Using ${theme} appearance${preference === 'system' ? ' to match your system' : ''}.`;
  }

  apply();
  system.addEventListener('change', apply);
  window.addEventListener('storage', event => {
    if (event.key === key || event.key === null) {
      preference = valid(event.newValue) ? event.newValue : 'system';
      apply();
    }
  });
  document.addEventListener('DOMContentLoaded', () => {
    apply();
    document.querySelector('#theme-select').addEventListener('change', event => {
      preference = event.target.value;
      try { localStorage.setItem(key, preference); } catch {}
      apply();
    });
  });
})();