dow) inset`;
        setTimeout(() => { el.style.boxShadow = old || '0 6px 20px var(--shadow) inset'; }, 120);
      }

      function blink(el) {
        const old = el.style.outline;
        el.style.outline = '3px solid var(--bad)';
        setTimeout(() => { el.style.outline = old; }, 140);
      }

      function getModeKey() {
        const ops = getSelectedOps().sort().join('');
        const diff = els.difficulty.value;
        const dur = parseInt(els.duration.value, 10);
        return `${diff}|${