/* ==========================================================================
   layout.css — page shell, container, section rhythm, site header & footer
   Mobile-first. Breakpoint overrides live in responsive.css.
   ========================================================================== */

/* ---- Page shell -------------------------------------------------------- */
.page {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

.page__main {
  flex: 1 0 auto;
}

.container {
  width: 100%;
  max-width: var(--container-width);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

/* ---- Section rhythm (45px / 10px, as on the reference) ----------------- */
.section {
  padding: var(--space-5) var(--space-2);
}

.section__title {
  font-size: var(--fs-2xl);
  text-transform: uppercase;
}

.section__intro {
  margin-top: var(--space-2);
  font-size: var(--fs-base);
}

/* ==========================================================================
   Site header
   ========================================================================== */
.site-header {
  position: relative;
  z-index: var(--z-header);
  background-color: var(--color-surface);
  box-shadow: var(--shadow-sm);
}

.site-header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  min-height: var(--header-height);
}

.site-header__logo {
  display: flex;
  align-items: center;
  gap: var(--space-2);
}

.site-header__logo-img {
  width: auto;
  height: 56px;
}

.site-header__tagline {
  display: flex;
  flex-direction: column;
  font-family: var(--font-heading);
  font-size: var(--fs-xs);
  font-weight: var(--fw-bold);
  line-height: 1.1;
  letter-spacing: 0.03em;
  text-transform: uppercase;
  color: var(--color-text);
}

.site-header__tagline-accent {
  color: var(--color-brand);
}

/* Hamburger (mobile only) */
.site-header__toggle {
  display: inline-flex;
  flex-direction: column;
  align-items: flex-end;
  justify-content: center;
  gap: 4px;
  width: 44px;
  height: 44px;
  padding: 0 var(--space-2);
}

.site-header__bar {
  display: block;
  width: 20px;
  height: 2px;
  background-color: var(--color-text);
  transition: transform var(--transition), opacity var(--transition);
}

.site-header__bar:nth-child(2) {
  width: 14px;
}

.site-header__toggle[aria-expanded="true"] .site-header__bar:nth-child(1) {
  transform: translateY(6px) rotate(45deg);
}

.site-header__toggle[aria-expanded="true"] .site-header__bar:nth-child(2) {
  opacity: 0;
}

.site-header__toggle[aria-expanded="true"] .site-header__bar:nth-child(3) {
  transform: translateY(-6px) rotate(-45deg);
}

/* Menu panel — a drop-down sheet on mobile */
.site-header__menu {
  position: absolute;
  top: 100%;
  left: 0;
  right: 0;
  display: none;
  flex-direction: column;
  max-height: calc(100vh - var(--header-height));
  overflow-y: auto;
  background-color: var(--color-surface);
  border-top: 1px solid var(--color-border-light);
  box-shadow: var(--shadow-menu);
}

.site-header__menu.is-open {
  display: flex;
}

.site-header__nav {
  order: 1;
}

.site-header__top {
  order: 2;
}

.site-header__link {
  display: flex;
  align-items: center;
  gap: var(--space-1);
  width: 100%;
  text-align: left;
  padding: var(--space-3);
  font-family: var(--font-heading);
  font-size: var(--fs-md);
  font-weight: var(--fw-medium);
  color: var(--color-text);
  border-bottom: 1px solid var(--color-border-light);
  transition: color var(--transition);
}

.site-header__link:hover,
.site-header__link[aria-current="page"] {
  color: var(--color-brand);
}

.site-header__link--accent {
  color: var(--color-brand);
}

.site-header__link i {
  font-size: var(--fs-xs);
}

/* Sub-menu items (Research, Sign In) */
.site-header__sublink {
  display: block;
  padding: var(--space-2) var(--space-3) var(--space-2) var(--space-4);
  font-size: var(--fs-base);
  color: var(--color-link);
  border-bottom: 1px solid var(--color-border-light);
}

.site-header__sublink:hover {
  color: var(--color-link-dark);
  background-color: var(--color-bg);
}

/* ==========================================================================
   Site footer
   ========================================================================== */
.site-footer {
  position: relative;
  padding: var(--space-5) 0 85px;
  color: var(--color-on-dark);
  background-image: linear-gradient(
    var(--color-footer-top),
    var(--color-footer-bottom) 50%,
    var(--color-footer-bottom)
  );
}

.site-footer__about {
  margin-bottom: var(--space-5);
}

.site-footer__heading {
  margin-bottom: var(--space-2);
  font-size: 20px;
  text-transform: uppercase;
  color: var(--color-on-dark);
}

.site-footer__about-text {
  font-size: var(--fs-xs);
  line-height: 1.6;
}

.site-footer__cols {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-4);
}

.site-footer__link {
  display: inline-block;
  font-weight: var(--fw-medium);
  line-height: 28px;
  color: var(--color-white);
}

.site-footer__link:hover {
  color: var(--color-white);
  text-decoration: underline;
}

.site-footer__article {
  margin-bottom: var(--space-3);
}

.site-footer__article-title {
  font-size: var(--fs-xs);
  font-weight: var(--fw-medium);
  line-height: 1.4;
  color: var(--color-white);
}

.site-footer__article-title:hover {
  color: var(--color-white);
  text-decoration: underline;
}

.site-footer__article-date {
  display: block;
  font-size: 10px;
  font-style: italic;
  color: var(--color-border);
}

.site-footer__social {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
}

/* Tagline with a rule on each side */
.site-footer__tagline {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  margin-top: var(--space-5);
  font-family: var(--font-heading);
  font-size: var(--fs-md);
  font-style: italic;
  font-weight: var(--fw-bold);
  text-align: center;
  text-transform: uppercase;
}

.site-footer__tagline::before,
.site-footer__tagline::after {
  content: "";
  flex: 1;
  height: 1px;
  background-color: var(--color-rule-on-dark);
}

.site-footer__tagline-accent {
  color: var(--color-brand-light);
}

.site-footer__legal-links {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: var(--space-4);
  margin-top: var(--space-4);
}

.site-footer__legal-text,
.site-footer__copy {
  margin-top: var(--space-4);
  font-size: var(--fs-xs);
  line-height: 1.6;
}

.site-footer__copy {
  margin-top: var(--space-3);
}

/* Back-to-top */
.back-to-top {
  position: fixed;
  right: var(--space-3);
  bottom: var(--space-3);
  z-index: var(--z-fixed);
  display: none;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  color: var(--color-white);
  background-color: var(--color-text);
  border-radius: var(--radius-pill);
  box-shadow: var(--shadow-menu);
  transition: background-color var(--transition);
}

.back-to-top.is-visible {
  display: inline-flex;
}

.back-to-top:hover {
  color: var(--color-white);
  background-color: var(--color-brand);
}