/* ---------- buttons ---------- */
.btn {
  --b-bg: var(--primary);
  --b-ink: var(--primary-ink);
  --b-edge: var(--primary-edge);
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  min-height: 48px;
  padding: 0 26px;
  border-radius: var(--r-pill);
  background: var(--b-bg);
  color: var(--b-ink);
  font-weight: 650;
  font-size: 17px;
  letter-spacing: 0.005em;
  text-decoration: none;
  white-space: nowrap;
  box-shadow: 0 4px 0 var(--b-edge);
  transform: translateY(0);
  transition: transform var(--t-fast) var(--ease), box-shadow var(--t-fast) var(--ease),
    background-color var(--t) var(--ease), opacity var(--t) var(--ease);
  user-select: none;
}
.btn:hover {
  transform: translateY(-1px);
  box-shadow: 0 5px 0 var(--b-edge);
}
.btn:active {
  transform: translateY(3px);
  box-shadow: 0 1px 0 var(--b-edge);
}
.btn[disabled],
.btn[aria-disabled="true"] {
  --b-bg: var(--surface-2);
  --b-ink: var(--ink-3);
  --b-edge: var(--line-2);
  cursor: not-allowed;
  transform: none;
}
.btn-secondary {
  --b-bg: var(--card);
  --b-ink: var(--ink);
  --b-edge: var(--line-2);
  border: 2px solid var(--line-2);
}
.btn-success {
  --b-bg: var(--success);
  --b-ink: #fff;
  --b-edge: #0b5d29;
}
.btn-error {
  --b-bg: var(--error);
  --b-ink: #fff;
  --b-edge: #8f2226;
}
:root[data-theme="dark"] .btn-success,
:root[data-theme="dark"] .btn-error {
  --b-ink: #22272e;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .btn-success,
  :root:not([data-theme="light"]) .btn-error {
    --b-ink: #22272e;
  }
}
.btn-ghost {
  background: transparent;
  color: var(--ink-2);
  box-shadow: none;
  padding: 0 14px;
  min-height: 44px;
}
.btn-ghost:hover {
  color: var(--ink);
  background: var(--surface);
  box-shadow: none;
  transform: none;
}
.btn-ghost:active {
  transform: none;
  box-shadow: none;
}
.btn-sm {
  min-height: 38px;
  padding: 0 16px;
  font-size: 15px;
}
.btn-block {
  width: 100%;
}

.icon-btn {
  display: inline-grid;
  place-items: center;
  width: 44px;
  height: 44px;
  border-radius: var(--r-pill);
  color: var(--ink-2);
  transition: background-color var(--t-fast) var(--ease), color var(--t-fast) var(--ease);
}
.icon-btn:hover {
  background: var(--surface);
  color: var(--ink);
}
.icon-btn svg {
  width: 22px;
  height: 22px;
}

/* ---------- pills / segmented ---------- */
.pills {
  display: inline-flex;
  flex-wrap: wrap;
  gap: 8px;
}
.pill {
  min-height: 40px;
  padding: 0 18px;
  border-radius: var(--r-pill);
  font-weight: 600;
  font-size: 15px;
  color: var(--ink-2);
  background: var(--card);
  border: 2px solid var(--line);
  transition: all var(--t-fast) var(--ease);
}
.pill:hover {
  color: var(--ink);
  border-color: var(--line-2);
}
.pill[aria-pressed="true"] {
  background: var(--ink);
  border-color: var(--ink);
  color: var(--bg);
}

.chip {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  height: 36px;
  padding: 0 12px;
  border-radius: var(--r-pill);
  font-weight: 700;
  font-size: 15px;
  font-variant-numeric: tabular-nums;
  background: var(--surface);
}
.chip svg {
  width: 18px;
  height: 18px;
}
.chip.streak.is-active {
  color: #e8590c;
  background: #fff1e6;
}
:root[data-theme="dark"] .chip.streak.is-active {
  background: #4a3a2c;
  color: #ff9d4d;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .chip.streak.is-active {
    background: #4a3a2c;
    color: #ff9d4d;
  }
}
.chip.xp {
  color: var(--select);
}

.tag {
  display: inline-flex;
  align-items: center;
  height: 22px;
  padding: 0 8px;
  border-radius: var(--r-pill);
  font-size: 11px;
  font-weight: 800;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  background: var(--success-bright);
  color: #0b2e16;
}

/* ---------- header ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: color-mix(in srgb, var(--bg) 86%, transparent);
  backdrop-filter: saturate(1.4) blur(14px);
  -webkit-backdrop-filter: saturate(1.4) blur(14px);
  border-bottom: 1px solid var(--line);
}
.site-header .wrap {
  display: flex;
  align-items: center;
  gap: 12px;
  height: var(--header-h);
}
.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  font-family: var(--font-display);
  font-weight: 600;
  font-size: 26px;
  letter-spacing: -0.02em;
}
.brand svg {
  width: 30px;
  height: 30px;
  flex: none;
}
.header-nav {
  display: flex;
  gap: 4px;
  margin-left: 16px;
}
.header-nav a {
  padding: 8px 12px;
  border-radius: var(--r-pill);
  text-decoration: none;
  font-weight: 600;
  font-size: 15px;
  color: var(--ink-2);
}
.header-nav a:hover,
.header-nav a[aria-current="page"] {
  color: var(--ink);
  background: var(--surface);
}
.header-right {
  margin-left: auto;
  display: flex;
  align-items: center;
  gap: 8px;
}
@media (max-width: 640px) {
  /* phones: the home page already lists the courses, so only About stays in the header */
  .header-nav {
    margin-left: 8px;
  }
  .header-nav a[href="#/courses"] {
    display: none;
  }
  .header-nav a {
    padding: 8px 10px;
  }
  .brand {
    font-size: 23px;
    gap: 8px;
  }
  .chip.xp {
    display: none;
  }
}

/* ---------- hero ---------- */
.hero {
  position: relative;
  padding: clamp(48px, 9vw, 104px) 0 clamp(40px, 6vw, 72px);
  overflow: hidden;
}
.hero .wrap {
  display: grid;
  grid-template-columns: 1.05fr 1fr;
  gap: 48px;
  align-items: center;
}
.hero h1 {
  font-family: var(--font-display);
  font-weight: 500;
  font-size: clamp(44px, 6.4vw, 76px);
  line-height: 1.02;
  letter-spacing: -0.025em;
}
.hero h1 em {
  font-style: italic;
  color: var(--blue);
}
.hero h1 em.phys {
  color: var(--coral);
}
.hero-sub {
  margin-top: 22px;
  font-size: clamp(18px, 2vw, 21px);
  color: var(--ink-2);
  max-width: 34ch;
}
.hero-cta {
  margin-top: 32px;
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}
.hero-art {
  position: relative;
  aspect-ratio: 1 / 0.9;
  border-radius: 32px;
  background: var(--surface);
  overflow: hidden;
}
.hero-art svg {
  width: 100%;
  height: 100%;
}
@media (max-width: 860px) {
  .hero .wrap {
    grid-template-columns: 1fr;
  }
  .hero-art {
    max-width: 520px;
    width: 100%;
  }
}

/* hero animation pieces */
.ha-float {
  animation: ha-float 7s var(--ease) infinite alternate;
  transform-box: fill-box;
  transform-origin: center;
}
.ha-float.d1 { animation-delay: -2s; animation-duration: 8s; }
.ha-spin {
  animation: ha-spin 24s linear infinite;
  transform-box: view-box;
}
.ha-trace {
  stroke-dasharray: 1;
  stroke-dashoffset: 1;
  animation: ha-trace 2.4s var(--ease) both;
}
.ha-pulse {
  animation: ha-pulse 2.6s var(--ease) infinite;
  transform-box: fill-box;
  transform-origin: center;
}
@keyframes ha-float {
  from { transform: translateY(-8px) rotate(-3deg); }
  to { transform: translateY(10px) rotate(4deg); }
}
@keyframes ha-spin {
  to { transform: rotate(360deg); }
}
@keyframes ha-trace {
  from { stroke-dashoffset: 1; }
  to { stroke-dashoffset: 0; }
}
@keyframes ha-pulse {
  0%, 100% { transform: scale(1); opacity: 1; }
  50% { transform: scale(1.35); opacity: 0.55; }
}

/* ---------- sections ---------- */
.section {
  padding: clamp(40px, 7vw, 88px) 0;
}
.section-head {
  display: flex;
  flex-wrap: wrap;
  align-items: end;
  justify-content: space-between;
  gap: 16px 24px;
  margin-bottom: 28px;
}
.section-title {
  font-family: var(--font-display);
  font-weight: 500;
  font-size: clamp(32px, 4.2vw, 48px);
  letter-spacing: -0.02em;
}
.section-sub {
  color: var(--ink-2);
  margin-top: 8px;
  max-width: 52ch;
}
.band {
  background: var(--surface);
}

/* ---------- tactile card ---------- */
.tcard {
  position: relative;
  display: block;
  background: var(--card);
  border: 2px solid var(--line);
  border-radius: var(--r-lg);
  box-shadow: 0 4px 0 var(--edge);
  text-decoration: none;
  color: inherit;
  transition: transform var(--t-fast) var(--ease), box-shadow var(--t-fast) var(--ease),
    border-color var(--t-fast) var(--ease);
}
a.tcard:hover,
button.tcard:hover {
  border-color: var(--line-2);
  transform: translateY(-2px);
  box-shadow: 0 6px 0 var(--edge);
}
a.tcard:active,
button.tcard:active {
  transform: translateY(3px);
  box-shadow: 0 1px 0 var(--edge);
}

/* ---------- course cards ---------- */
.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 22px;
}
.course-card {
  display: flex;
  flex-direction: column;
  overflow: hidden;
}
.course-card .cover {
  aspect-ratio: 16 / 10;
  background: var(--cc-soft, var(--surface));
  border-bottom: 2px solid var(--line);
  overflow: hidden;
}
.course-card .cover svg {
  width: 100%;
  height: 100%;
  transition: transform var(--t-slow) var(--ease-out);
}
.course-card:hover .cover svg {
  transform: scale(1.04);
}
.course-card .body {
  padding: 16px 18px 18px;
  display: flex;
  flex-direction: column;
  gap: 6px;
  flex: 1;
}
.course-card h3 {
  font-size: 20px;
  font-weight: 700;
  letter-spacing: -0.01em;
}
.course-card .tagline {
  color: var(--ink-2);
  font-size: 15px;
  line-height: 1.45;
}
.course-card .meta {
  margin-top: auto;
  padding-top: 12px;
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 13px;
  font-weight: 600;
  color: var(--ink-3);
}
.progress {
  flex: 1;
  height: 8px;
  border-radius: var(--r-pill);
  background: var(--surface-2);
  overflow: hidden;
}
.progress > span {
  display: block;
  height: 100%;
  width: 0;
  border-radius: inherit;
  background: var(--cc, var(--success-bright));
  transition: width var(--t-slow) var(--ease-out);
}
.subject-math {
  --cc: var(--blue);
  --cc-soft: var(--blue-soft);
}
.subject-physics {
  --cc: var(--coral);
  --cc-soft: var(--coral-soft);
}

/* ---------- continue card ---------- */
.continue-card {
  display: grid;
  grid-template-columns: 120px 1fr auto;
  align-items: center;
  gap: 20px;
  padding: 16px;
}
.continue-card .cover {
  width: 120px;
  aspect-ratio: 16 / 11;
  border-radius: var(--r-md);
  overflow: hidden;
  background: var(--cc-soft);
}
.continue-card .cover svg {
  width: 100%;
  height: 100%;
}
.continue-card h3 {
  font-size: 20px;
  margin: 4px 0 2px;
}
@media (max-width: 600px) {
  .continue-card {
    grid-template-columns: 84px 1fr;
  }
  .continue-card .cover {
    width: 84px;
  }
  .continue-card .btn {
    grid-column: 1 / -1;
  }
}

/* ---------- principles ---------- */
.principles {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 22px;
}
@media (max-width: 1040px) {
  .principles {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}
@media (max-width: 560px) {
  .principles {
    grid-template-columns: 1fr;
  }
}
.principle {
  padding: 24px;
}
.principle .art {
  height: 120px;
  margin: -4px -4px 16px;
  border-radius: var(--r-md);
  background: var(--surface);
  overflow: hidden;
}
.principle .art svg {
  width: 100%;
  height: 100%;
}
.principle h3 {
  font-size: 20px;
  margin-bottom: 6px;
}
.principle p {
  color: var(--ink-2);
  font-size: 16px;
}

/* ---------- course page ---------- */
.course-hero {
  padding: 36px 0 28px;
}
.course-hero .wrap {
  display: grid;
  grid-template-columns: 1fr 380px;
  gap: 40px;
  align-items: center;
}
.course-hero h1 {
  font-family: var(--font-display);
  font-weight: 500;
  font-size: clamp(40px, 5.4vw, 60px);
  letter-spacing: -0.02em;
  margin: 8px 0 12px;
}
.course-hero .desc {
  color: var(--ink-2);
  font-size: 18px;
  max-width: 54ch;
}
.course-hero .cover {
  border-radius: var(--r-xl);
  overflow: hidden;
  aspect-ratio: 16 / 11;
  background: var(--cc-soft);
}
.course-hero .cover svg {
  width: 100%;
  height: 100%;
}
.course-stats {
  display: flex;
  flex-wrap: wrap;
  gap: 10px 22px;
  margin: 18px 0 24px;
  font-weight: 600;
  color: var(--ink-2);
  font-size: 15px;
}
.course-stats span {
  display: inline-flex;
  align-items: center;
  gap: 6px;
}
.course-stats svg {
  width: 18px;
  height: 18px;
}
.back-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-weight: 600;
  font-size: 15px;
  color: var(--ink-2);
  text-decoration: none;
}
.back-link:hover {
  color: var(--ink);
}
.back-link svg {
  width: 18px;
  height: 18px;
}
@media (max-width: 860px) {
  .course-hero .wrap {
    grid-template-columns: 1fr;
  }
  .course-hero .cover {
    order: -1;
    max-width: 440px;
  }
}

/* path */
.chapters {
  max-width: 760px;
  margin: 0 auto;
  padding-bottom: 80px;
}
.chapter {
  margin-top: 40px;
}
.chapter-head {
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 16px 20px;
  border-radius: var(--r-lg);
  background: var(--surface);
}
.chapter-head .num {
  display: grid;
  place-items: center;
  width: 40px;
  height: 40px;
  border-radius: 12px;
  background: var(--cc);
  color: #fff;
  font-weight: 800;
  flex: none;
}
.chapter-head h2 {
  font-size: 20px;
}
.chapter-head p {
  font-size: 14px;
  color: var(--ink-2);
  margin: 2px 0 0;
}
.path {
  position: relative;
  padding: 18px 0 0;
  list-style: none;
  margin: 0;
}
.path-item {
  position: relative;
  display: grid;
  grid-template-columns: 240px 1fr;
  align-items: center;
  gap: 8px;
  padding: 12px 0;
}
.node-col {
  display: flex;
  justify-content: center;
  transform: translateX(calc(var(--off, 0) * 44px));
}
.path-svg {
  position: absolute;
  left: 0;
  top: 0;
  pointer-events: none;
  overflow: visible;
  z-index: 0;
}
.path-svg path {
  fill: none;
  stroke: var(--line-2);
  stroke-width: 4;
  stroke-dasharray: 1 12;
  stroke-linecap: round;
}
.node {
  position: relative;
  z-index: 1;
  display: grid;
  place-items: center;
  width: 76px;
  height: 72px;
  border-radius: 50%;
  background: var(--card);
  border: 2px solid var(--line-2);
  box-shadow: 0 6px 0 var(--edge);
  color: var(--ink-3);
  transition: transform var(--t-fast) var(--ease), box-shadow var(--t-fast) var(--ease);
}
.node svg {
  width: 28px;
  height: 28px;
}
.node:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 0 var(--edge);
}
.node:active {
  transform: translateY(5px);
  box-shadow: 0 1px 0 var(--edge);
}
.node.is-done {
  background: var(--cc);
  border-color: transparent;
  color: #fff;
  box-shadow: 0 6px 0 color-mix(in srgb, var(--cc) 55%, #000);
}
.node.is-next {
  border-color: var(--cc);
  border-width: 3px;
  color: var(--cc);
}
.node.is-next::after {
  content: "";
  position: absolute;
  inset: -10px;
  border-radius: 50%;
  border: 3px solid var(--cc);
  opacity: 0.35;
  animation: node-ring 2s var(--ease) infinite;
}
@keyframes node-ring {
  0% { transform: scale(0.92); opacity: 0.5; }
  100% { transform: scale(1.18); opacity: 0; }
}
.node-label {
  text-decoration: none;
  min-width: 0;
}
.node-label strong {
  display: block;
  font-size: 18px;
  line-height: 1.25;
}
.node-label span {
  display: block;
  margin-top: 2px;
  font-size: 14px;
  color: var(--ink-3);
  line-height: 1.35;
}
.node-label:hover strong {
  text-decoration: underline;
  text-underline-offset: 3px;
}
@media (max-width: 600px) {
  .path-item {
    grid-template-columns: 150px 1fr;
  }
  .node-col {
    transform: translateX(calc(var(--off, 0) * 22px));
  }
  .node {
    width: 64px;
    height: 60px;
  }
}

/* ---------- footer ---------- */
.site-footer {
  border-top: 1px solid var(--line);
  padding: 40px 0 56px;
  color: var(--ink-3);
  font-size: 14px;
}
.site-footer .wrap {
  display: flex;
  flex-wrap: wrap;
  gap: 12px 24px;
  justify-content: space-between;
}

/* ---------- toast ---------- */
.toast {
  position: fixed;
  left: 50%;
  bottom: 24px;
  transform: translate(-50%, 20px);
  opacity: 0;
  padding: 12px 18px;
  border-radius: var(--r-pill);
  background: var(--ink);
  color: var(--bg);
  font-weight: 600;
  box-shadow: var(--shadow-pop);
  transition: all var(--t) var(--spring);
  z-index: 200;
  pointer-events: none;
}
.toast.show {
  opacity: 1;
  transform: translate(-50%, 0);
}

/* page enter */
.page-enter {
  animation: page-in var(--t-slow) var(--ease-out) both;
}
@keyframes page-in {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: none; }
}

/* catalogue grouped by level */
.catalog {
  display: grid;
  gap: 18px;
}
.level-head {
  display: flex;
  align-items: baseline;
  gap: 12px;
  margin-top: 18px;
  padding-bottom: 8px;
  border-bottom: 2px solid var(--line);
}
.level-head .eyebrow {
  font-size: 13px;
  color: var(--ink-2);
}
.level-count {
  font-size: 13px;
  color: var(--ink-3);
  font-weight: 600;
}

/* ---------- catalogue filters ---------- */
.filters {
  display: grid;
  gap: 10px;
}
.filter-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px 14px;
}
.filter-label {
  min-width: 78px;
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--ink-3);
}

/* ---------- about ---------- */
.about {
  padding-top: clamp(40px, 7vw, 88px);
  padding-bottom: 72px;
  max-width: 980px;
}
.about-title {
  margin-top: 14px;
  font-family: var(--font-display);
  font-weight: 500;
  font-size: clamp(38px, 6vw, 64px);
  line-height: 1.05;
  letter-spacing: -0.02em;
}
.about-title em {
  color: var(--coral);
}
.about-lead {
  margin-top: 22px;
  max-width: 640px;
  font-size: clamp(18px, 2.2vw, 21px);
  line-height: 1.55;
  color: var(--ink-2);
}
.about-stats {
  margin-top: 36px;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: 12px;
}
.about-stats > div {
  padding: 18px 20px;
  border-radius: var(--r-lg);
  background: var(--surface);
}
.about-stats b {
  display: block;
  font-family: var(--font-display);
  font-size: 34px;
  font-weight: 600;
  line-height: 1.1;
}
.about-stats span {
  font-size: 15px;
  color: var(--ink-2);
}
.about-grid {
  margin-top: 28px;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 16px;
}
.about-grid .tcard {
  padding: 24px;
}
.about-grid h3 {
  font-size: 20px;
  margin-bottom: 8px;
}
.about-grid p {
  color: var(--ink-2);
  line-height: 1.6;
}
.about-cta {
  margin-top: 36px;
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

/* ---------- impressum & privacy ---------- */
.legal {
  padding-top: clamp(40px, 7vw, 88px);
  padding-bottom: 72px;
  max-width: 720px;
}
.legal h1 {
  font-family: var(--font-display);
  font-weight: 500;
  font-size: clamp(32px, 5vw, 44px);
}
.legal h2 {
  margin-top: 36px;
  font-size: 22px;
}
.legal p {
  margin-top: 14px;
  color: var(--ink-2);
  line-height: 1.6;
}
@media (max-width: 360px) {
  /* very narrow phones: the logo alone leaves room for About, the streak and the theme switch */
  .brand span {
    position: absolute;
    width: 1px;
    height: 1px;
    overflow: hidden;
    clip: rect(0 0 0 0);
  }
}