@media (max-width: 900px) {
  .hero-section,
  .calculator-layout {
    grid-template-columns: 1fr;
  }
  .main-nav {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    width: 100%;
    background: var(--bg-solid);
    padding: 1rem;
    border-bottom: 1px solid var(--border);
    flex-direction: column;
  }
  .main-nav.open { display: flex; }
  .menu-toggle { display: inline-flex; }
}

@media (max-width: 640px) {
  .container { width: min(100% - 1rem, 1180px); }
  .hero-section { padding-top: 2rem; }
  .section-block { padding: 3rem 0; }
  .topbar-inner, .nav-wrap { align-items: center; }
  .form-grid { grid-template-columns: 1fr; }
  .result-heading { flex-direction: column; align-items: flex-start; }
}