:root {
  color-scheme: dark;
  --bg: #030303;
  --panel: #0b0b0d;
  --panel-soft: #111113;
  --ink: #e6e6e6;
  --ink-strong: #ffffff;
  --muted: #a0a0a0;
  --line: #202020;
  --line-strong: #343434;
  --accent: #4b9fe8;
  --accent-ink: #050505;
  --navy: #f1f1f1;
  --gray-button: #151515;
  --input-bg: #050505;
  --track-bg: #242424;
  --hover-bg: #121212;
  --active-bg: #151515;
  --nested-bg: #070707;
  --pill-bg: #171717;
  --scroll-track: #050505;
  --scroll-thumb: #3a3a3a;
  --shadow: 0 8px 18px #000000;
  --sidebar-width: 16.25rem;
  --sidebar-collapsed-width: 4.5rem;
  --playlist-width: clamp(21.25rem, 24vw, 26.25rem);
  font-family: Montserrat, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

:root[data-theme="light"] {
  color-scheme: light;
  --bg: #f4f4f4;
  --panel: #ffffff;
  --panel-soft: #eeeeee;
  --ink: #1f1f1f;
  --ink-strong: #050505;
  --muted: #696969;
  --line: #dddddd;
  --line-strong: #c8c8c8;
  --accent: #1f7fc9;
  --accent-ink: #ffffff;
  --navy: #202020;
  --gray-button: #eeeeee;
  --input-bg: #ffffff;
  --track-bg: #dddddd;
  --hover-bg: #f6f6f6;
  --active-bg: #f1f1f1;
  --nested-bg: #f7f7f7;
  --pill-bg: #eeeeee;
  --scroll-track: #efefef;
  --scroll-thumb: #bdbdbd;
  --shadow: 0 8px 18px #d7d7d7;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
}

button,
input {
  font: inherit;
}

.app-shell {
  display: grid;
  grid-template-columns: var(--sidebar-width) minmax(0, 1fr);
  min-height: 100vh;
}

.app-shell.has-playlist {
  grid-template-columns: var(--sidebar-width) minmax(0, 1fr) var(--playlist-width);
}

.app-shell.is-sidebar-collapsed {
  --sidebar-width: var(--sidebar-collapsed-width);
}

.course-sidebar {
  position: sticky;
  top: 0;
  align-self: start;
  height: 100vh;
  overflow-y: auto;
  border-right: 1px solid var(--line);
  background: var(--panel);
  padding: 0;
}

.course-sidebar::-webkit-scrollbar {
  width: 10px;
}

.course-sidebar::-webkit-scrollbar-track {
  background: var(--scroll-track);
}

.course-sidebar::-webkit-scrollbar-thumb {
  border: 3px solid var(--scroll-track);
  border-radius: 999px;
  background: var(--scroll-thumb);
}

.brand-lockup {
  display: flex;
  gap: 0.95rem;
  align-items: center;
  padding: 1.1rem;
  border-bottom: 1px solid var(--line);
  background: var(--panel);
}

.brand-copy {
  min-width: 0;
}

.sidebar-toggle {
  display: grid;
  place-items: center;
  width: 2rem;
  height: 2rem;
  margin-left: auto;
  border: 1px solid var(--line-strong);
  border-radius: 999px;
  background: var(--gray-button);
  color: var(--ink);
  cursor: pointer;
  font-size: 1.1rem;
  line-height: 1;
}

.mobile-menu-button,
.sidebar-backdrop {
  display: none;
}

.app-shell.is-sidebar-collapsed .brand-lockup {
  justify-content: center;
  padding: 0.95rem 0.6rem;
}

.app-shell.is-sidebar-collapsed .brand-logo {
  width: 3rem;
  height: 3rem;
}

.app-shell.is-sidebar-collapsed .brand-copy,
.app-shell.is-sidebar-collapsed .theme-row,
.app-shell.is-sidebar-collapsed .progress-card,
.app-shell.is-sidebar-collapsed .search-label,
.app-shell.is-sidebar-collapsed .course-search,
.app-shell.is-sidebar-collapsed .tree-title,
.app-shell.is-sidebar-collapsed .tree-meta,
.app-shell.is-sidebar-collapsed .tree-children {
  display: none;
}

.app-shell.is-sidebar-collapsed .sidebar-toggle {
  position: absolute;
  top: 4.35rem;
  left: 50%;
  width: 1.8rem;
  height: 1.8rem;
  margin-left: 0;
  transform: translateX(-50%) rotate(180deg);
}

.app-shell.is-sidebar-collapsed .course-tree {
  padding-top: 2.7rem;
}

.app-shell.is-sidebar-collapsed .tree-row {
  display: grid;
  grid-template-columns: 1fr;
  justify-items: center;
  min-height: 2.7rem;
  padding: 0.4rem;
}

.app-shell.is-sidebar-collapsed .tree-toggle {
  width: 1.6rem;
  height: 1.6rem;
  border-radius: 999px;
  background: var(--panel-soft);
}

.theme-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  border-bottom: 1px solid var(--line);
  background: var(--panel);
  padding: 0.85rem 1.1rem;
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.theme-toggle {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  border: 1px solid var(--line-strong);
  border-radius: 999px;
  background: var(--gray-button);
  color: var(--ink);
  padding: 0.3rem 0.55rem 0.3rem 0.35rem;
  cursor: pointer;
  font-size: 0.78rem;
  font-weight: 600;
}

.theme-toggle-track {
  position: relative;
  display: inline-block;
  width: 2.1rem;
  height: 1.15rem;
  border-radius: 999px;
  background: #2c2c2c;
}

.theme-toggle-thumb {
  position: absolute;
  top: 0.18rem;
  left: 0.18rem;
  width: 0.79rem;
  height: 0.79rem;
  border-radius: 999px;
  background: var(--accent);
  transition: left 160ms ease;
}

:root[data-theme="light"] .theme-toggle-track {
  background: #d0d0d0;
}

:root[data-theme="light"] .theme-toggle-thumb {
  left: 1.13rem;
}

.brand-logo {
  display: block;
  width: 4.35rem;
  height: 4.35rem;
  flex: 0 0 auto;
  border: 1px solid var(--line-strong);
  border-radius: 999px;
  object-fit: cover;
  object-position: center;
}

.eyebrow {
  margin: 0 0 0.16rem;
  color: var(--muted);
  font-size: 0.68rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

h1,
h2,
h3,
p {
  margin-top: 0;
}

h1 {
  margin-bottom: 0;
  color: var(--ink-strong);
  font-size: 1.08rem;
  font-weight: 700;
  letter-spacing: 0.02em;
  line-height: 1.15;
  text-transform: uppercase;
}

h2 {
  margin-bottom: 0;
  color: var(--ink-strong);
  font-size: clamp(1.45rem, 2vw, 2.25rem);
  font-weight: 650;
  letter-spacing: 0;
  line-height: 1.12;
}

h3 {
  margin-bottom: 0.85rem;
  color: var(--navy);
  font-size: 0.9rem;
  letter-spacing: 0.05em;
  font-weight: 600;
  text-transform: uppercase;
}

.progress-card {
  margin: 0;
  border: 0;
  border-bottom: 1px solid var(--line);
  border-radius: 0;
  background: var(--panel-soft);
  padding: 0.95rem 1.1rem;
}

.progress-copy {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  color: var(--muted);
  font-size: 0.82rem;
  font-weight: 600;
}

.progress-copy span:first-child {
  color: var(--ink-strong);
}

.progress-track {
  height: 0.5rem;
  margin: 0.7rem 0 0.85rem;
  overflow: hidden;
  border-radius: 999px;
  background: var(--track-bg);
}

.progress-track span {
  display: block;
  width: 0%;
  height: 100%;
  border-radius: inherit;
  background: var(--accent);
  transition: width 180ms ease;
}

.sidebar-actions,
.lesson-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
}

.mobile-lesson-progress {
  display: none;
}

.mobile-module-panel {
  display: none;
}

.button {
  min-height: 2.35rem;
  border: 1px solid transparent;
  border-radius: 8px;
  padding: 0.58rem 0.88rem;
  cursor: pointer;
  font-weight: 600;
  transition: transform 140ms ease, border-color 140ms ease, box-shadow 140ms ease, background 140ms ease;
}

.button:hover:not(:disabled) {
  border-color: #555555;
  box-shadow: none;
}

.button:disabled {
  cursor: not-allowed;
  border-color: #252525;
  background: #111111;
  color: #6b6b6b;
}

.button-primary {
  background: var(--accent);
  color: var(--accent-ink);
}

.button-secondary,
.button-ghost {
  border-color: var(--line-strong);
  background: var(--gray-button);
  color: var(--ink);
}

.search-label {
  display: block;
  padding: 0.85rem 1.1rem 0.42rem;
  color: var(--muted);
  font-size: 0.68rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.course-search {
  width: calc(100% - 2.2rem);
  margin: 0 1.1rem 0.85rem;
  border: 1px solid var(--line-strong);
  border-radius: 8px;
  background: var(--input-bg);
  padding: 0.72rem 0.8rem;
  color: var(--ink);
}

.course-search::placeholder {
  color: #747474;
}

.course-search:focus {
  outline: 3px solid #202020;
  border-color: #666666;
}

:root[data-theme="light"] .course-search:focus {
  outline-color: #dddddd;
}

.course-tree {
  display: grid;
  gap: 0;
  padding-bottom: 3rem;
  border-top: 1px solid var(--line);
}

.tree-node {
  display: grid;
  gap: 0;
}

.tree-row {
  position: relative;
  display: grid;
  grid-template-columns: 1.05rem minmax(0, 1fr) auto;
  align-items: center;
  gap: 0.55rem;
  width: 100%;
  min-height: 2.35rem;
  border: 0;
  border-bottom: 1px solid var(--line);
  border-radius: 0;
  background: var(--panel);
  padding: 0.48rem 0.9rem;
  color: var(--ink);
  text-align: left;
}

.tree-row::before {
  display: none;
}

.tree-row:hover {
  background: var(--hover-bg);
}

.tree-row[aria-current="true"] {
  background: var(--active-bg);
  box-shadow: inset 3px 0 0 var(--accent);
}

.tree-toggle {
  display: grid;
  place-items: center;
  width: 1.05rem;
  height: 1.05rem;
  color: #bdbdbd;
  font-size: 1.05rem;
  font-weight: 600;
  line-height: 1;
  transition: transform 160ms ease;
}

.tree-row[data-open="true"] .tree-toggle {
  transform: rotate(90deg);
}

.tree-row[data-node-type="lesson"] .tree-toggle {
  color: #8c8c8c;
  font-size: 0.9rem;
}

.tree-title {
  overflow: hidden;
  color: var(--ink-strong);
  text-overflow: ellipsis;
  white-space: nowrap;
  font-size: 0.9rem;
  font-weight: 600;
}

.tree-row[data-node-type="lesson"] .tree-title {
  color: #cfcfcf;
  font-weight: 500;
}

.tree-row.is-coming-soon .tree-title {
  color: var(--muted);
  font-weight: 500;
}

.tree-meta {
  color: var(--muted);
  font-size: 0.76rem;
  font-variant-numeric: tabular-nums;
  font-weight: 500;
}

.tree-row[data-node-type="lesson"] .tree-meta {
  color: #a8a8a8;
}

.tree-children {
  display: none;
  margin-left: 0;
  padding-left: 1.1rem;
  border-left: 0;
  background: var(--nested-bg);
}

.tree-children.is-open {
  display: grid;
  gap: 0;
}

.tree-row.is-complete .tree-title::after {
  content: " complete";
  color: #cfcfcf;
  font-size: 0.65rem;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.empty-note {
  margin: 0;
  border-bottom: 1px solid var(--line);
  background: var(--nested-bg);
  padding: 0.38rem 1rem 0.48rem 3.15rem;
  color: var(--muted);
  font-size: 0.78rem;
}

.lesson-main {
  min-width: 0;
  display: flex;
  flex-direction: column;
  padding: clamp(0.85rem, 1.8vw, 1.45rem);
}

.lesson-hero,
.player-panel,
.lesson-details article {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  box-shadow: var(--shadow);
}

.lesson-hero {
  position: relative;
  overflow: hidden;
  margin-bottom: 0.75rem;
  padding: 0.85rem 1rem;
  background: var(--panel);
}

.lesson-topline {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
  align-items: center;
  margin-bottom: 0.42rem;
}

.back-button {
  position: fixed;
  z-index: 18;
  bottom: 1rem;
  left: calc(var(--sidebar-width) + 1rem);
  display: grid;
  place-items: center;
  width: 2.6rem;
  height: 2.6rem;
  min-height: 0;
  border: 1px solid var(--line-strong);
  border-radius: 999px;
  background: var(--gray-button);
  color: var(--ink);
  padding: 0;
  cursor: pointer;
  font-size: 1.25rem;
  font-weight: 600;
  box-shadow: var(--shadow);
}

.back-button:hover {
  border-color: #555555;
}

.lesson-kicker {
  margin-bottom: 0;
  color: var(--muted);
  font-size: 0.68rem;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.lesson-header {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 0.85rem;
  align-items: center;
}

.lesson-header p {
  max-width: 64rem;
  margin-bottom: 0;
  color: var(--muted);
  font-size: 1rem;
  line-height: 1.6;
}

[hidden] {
  display: none !important;
}

.skill-hub {
  display: grid;
  gap: 1rem;
  margin-bottom: 1rem;
}

.hub-header {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  align-items: end;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  padding: 0.85rem 1rem;
  box-shadow: var(--shadow);
}

.hub-title {
  margin-bottom: 0;
  color: var(--ink-strong);
  font-size: 1rem;
  letter-spacing: 0;
  text-transform: none;
}

.hub-description {
  max-width: 46rem;
  margin-bottom: 0;
  color: var(--muted);
  line-height: 1.55;
}

.hub-resume {
  flex: 0 0 auto;
}

.skill-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(13rem, 1fr));
  gap: 0.65rem;
}

.skill-card {
  position: relative;
  display: grid;
  grid-template-rows: minmax(0, 1fr) auto;
  gap: 0.8rem;
  min-height: 6.5rem;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  padding: 0.95rem;
  color: var(--ink);
  text-align: left;
  cursor: pointer;
  box-shadow: var(--shadow);
  transition: border-color 160ms ease, box-shadow 160ms ease;
}

.skill-card::after {
  display: none;
}

.skill-card:hover {
  border-color: var(--line-strong);
  box-shadow: var(--shadow);
}

.skill-card[data-node-type="lesson"] {
  background: var(--panel);
}

.skill-card-eyebrow {
  color: var(--muted);
  font-size: 0.72rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.skill-card-title {
  position: relative;
  z-index: 1;
  max-width: 100%;
  color: var(--ink-strong);
  font-size: 0.98rem;
  line-height: 1.25;
  letter-spacing: -0.01em;
  font-weight: 600;
}

.skill-card-description {
  position: relative;
  z-index: 1;
  color: var(--muted);
  font-size: 0.93rem;
  line-height: 1.48;
}

.skill-card-footer {
  position: relative;
  z-index: 1;
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  align-items: center;
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 600;
}

.hub-empty {
  margin: 0;
  border: 1px dashed var(--line-strong);
  border-radius: 14px;
  background: var(--panel);
  padding: 1.4rem;
  color: var(--muted);
}

.lesson-status {
  border: 1px solid var(--line-strong);
  border-radius: 999px;
  background: var(--pill-bg);
  color: var(--ink);
  padding: 0.42rem 0.68rem;
  font-size: 0.76rem;
  font-weight: 600;
  white-space: nowrap;
}

.course-playlist {
  display: grid;
  gap: 0.65rem;
  margin: 0;
  border: 0;
  border-radius: 0;
  background: transparent;
  padding: 0;
  box-shadow: none;
}

.playlist-panel {
  position: sticky;
  top: 0;
  align-self: start;
  height: 100vh;
  overflow-y: auto;
  border-left: 1px solid var(--line);
  background: var(--panel);
  padding: 0.9rem;
}

.playlist-panel[hidden] {
  display: none !important;
}

.playlist-panel::-webkit-scrollbar {
  width: 10px;
}

.playlist-panel::-webkit-scrollbar-track {
  background: var(--scroll-track);
}

.playlist-panel::-webkit-scrollbar-thumb {
  border: 3px solid var(--scroll-track);
  border-radius: 999px;
  background: var(--scroll-thumb);
}

.playlist-header {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 0.75rem;
  align-items: start;
  border-bottom: 1px solid var(--line);
  padding-bottom: 0.7rem;
}

.playlist-heading {
  min-width: 0;
}

.playlist-eyebrow {
  margin: 0 0 0.2rem;
  color: var(--muted);
  font-size: 0.62rem;
  font-weight: 650;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.playlist-title {
  margin-bottom: 0;
  color: var(--ink-strong);
  font-size: 0.98rem;
  letter-spacing: 0;
  text-transform: none;
  line-height: 1.25;
}

.playlist-count {
  justify-self: end;
  border: 1px solid var(--line-strong);
  border-radius: 999px;
  background: var(--pill-bg);
  color: var(--muted);
  padding: 0.35rem 0.5rem;
  font-size: 0.72rem;
  font-weight: 600;
  white-space: nowrap;
}

.playlist-toggle {
  display: none;
}

.playlist-summary {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
}

.playlist-summary span {
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--panel-soft);
  color: var(--muted);
  padding: 0.32rem 0.5rem;
  font-size: 0.72rem;
  font-weight: 600;
}

.playlist-progress {
  height: 0.42rem;
  overflow: hidden;
  border-radius: 999px;
  background: var(--track-bg);
}

.playlist-progress span {
  display: block;
  height: 100%;
  border-radius: inherit;
  background: var(--accent);
}

.playlist-list {
  display: grid;
  gap: 0.38rem;
}

.playlist-row {
  display: grid;
  grid-template-columns: 2rem minmax(0, 1fr);
  gap: 0.55rem 0.65rem;
  align-items: start;
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel-soft);
  padding: 0.68rem 0.72rem;
  color: var(--ink);
  text-align: left;
  cursor: pointer;
}

.playlist-row:hover {
  border-color: var(--line-strong);
  background: var(--hover-bg);
}

.playlist-row[aria-current="true"] {
  border-color: var(--line-strong);
  background: var(--active-bg);
  box-shadow: inset 3px 0 0 var(--accent);
}

.playlist-number,
.playlist-row-status {
  color: var(--muted);
  font-size: 0.76rem;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
}

.playlist-row-title {
  color: var(--ink-strong);
  font-size: 0.86rem;
  font-weight: 600;
  line-height: 1.3;
}

.playlist-row-status {
  grid-column: 2;
}

.playlist-row.is-complete .playlist-row-status {
  color: var(--ink);
}

.playlist-row.is-coming-soon .playlist-row-title,
.playlist-row.is-coming-soon .playlist-number,
.playlist-row.is-coming-soon .playlist-row-status {
  color: var(--muted);
  font-weight: 500;
}

.player-panel {
  display: grid;
  place-items: center;
  overflow: hidden;
  margin-bottom: 0.75rem;
  background: #050505;
  padding: clamp(0.55rem, 1.2vw, 0.9rem);
}

.video-shell {
  position: relative;
  display: grid;
  place-items: center;
  width: min(100%, 64rem);
  max-height: calc(100vh - 11rem);
  min-height: 20rem;
  overflow: hidden;
  aspect-ratio: 16 / 9;
  border: 1px solid #222222;
  border-radius: 8px;
  background: #000000;
  background-position: center;
  background-size: cover;
  color: #fff;
}

.video-shell iframe {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  border: 0;
  background: #000;
}

.video-placeholder {
  position: relative;
  z-index: 1;
  display: grid;
  justify-items: center;
  gap: 0.75rem;
  max-width: 26rem;
  padding: 2rem;
  text-align: center;
}

.video-load-button .video-placeholder {
  border: 1px solid #303030;
  border-radius: 8px;
  background: #050505;
  padding: 1rem 1.2rem;
}

.video-placeholder p {
  margin-bottom: 0;
  color: #fff;
  font-size: 0.9rem;
  font-weight: 600;
  line-height: 1.45;
}

.video-note {
  display: block;
  max-width: 22rem;
  color: #b8b8b8;
  font-size: 0.78rem;
  font-weight: 500;
  line-height: 1.45;
}

.play-badge {
  width: 3.45rem;
  height: 3.45rem;
  border: 1px solid #fff;
  border-radius: 999px;
  background: #fff;
  box-shadow: none;
}

.play-badge::after {
  content: "";
  display: block;
  width: 0;
  height: 0;
  margin: 0.98rem 0 0 1.38rem;
  border-top: 0.7rem solid transparent;
  border-bottom: 0.7rem solid transparent;
  border-left: 1rem solid #111111;
}

.video-load-button {
  border: 0;
  background-color: #050505;
  color: inherit;
  cursor: pointer;
}

.lesson-actions {
  order: 3;
  margin-bottom: 0.75rem;
}

.lesson-details {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.9rem;
}

.lesson-details article {
  padding: 1.15rem;
}

.detail-list {
  display: grid;
  gap: 0.65rem;
  margin: 0;
  padding-left: 1.05rem;
  color: var(--muted);
  line-height: 1.55;
}

.detail-list li::marker {
  color: #9a9a9a;
}

.tag-list {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  margin-top: 1rem;
}

.tag {
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--pill-bg);
  color: var(--ink);
  padding: 0.32rem 0.52rem;
  font-size: 0.75rem;
  font-weight: 600;
}

@media (max-width: 920px) {
  .app-shell {
    display: block;
  }

  .course-sidebar {
    position: fixed;
    z-index: 30;
    inset: 0 auto 0 0;
    width: min(86vw, 21rem);
    height: 100vh;
    max-height: none;
    border-right: 1px solid var(--line);
    border-bottom: 0;
    transform: translateX(-102%);
    transition: transform 180ms ease;
  }

  .app-shell.is-sidebar-open .course-sidebar {
    transform: translateX(0);
  }

  .sidebar-backdrop {
    position: fixed;
    z-index: 20;
    inset: 0;
    display: none;
    border: 0;
    background: rgba(0, 0, 0, 0.64);
  }

  .app-shell.is-sidebar-open .sidebar-backdrop {
    display: block;
  }

  .mobile-menu-button {
    display: inline-grid;
    place-items: center;
    gap: 0.18rem;
    width: 2.35rem;
    height: 2.35rem;
    min-height: 0;
    margin-bottom: 0.55rem;
    border: 1px solid var(--line-strong);
    border-radius: 8px;
    background: var(--gray-button);
    color: var(--ink);
    padding: 0;
    cursor: pointer;
  }

  .mobile-menu-button span {
    display: block;
    width: 1.05rem;
    height: 0.1rem;
    border-radius: 999px;
    background: currentColor;
  }

  .app-shell.is-sidebar-collapsed .brand-lockup {
    justify-content: flex-start;
    padding: 1.1rem;
  }

  .app-shell.is-sidebar-collapsed .brand-logo {
    width: 4.35rem;
    height: 4.35rem;
  }

  .app-shell.is-sidebar-collapsed .brand-copy,
  .app-shell.is-sidebar-collapsed .tree-title,
  .app-shell.is-sidebar-collapsed .tree-meta {
    display: block;
  }

  .app-shell.is-sidebar-collapsed .theme-row,
  .app-shell.is-sidebar-collapsed .progress-card {
    display: flex;
  }

  .app-shell.is-sidebar-collapsed .progress-card {
    display: block;
  }

  .app-shell.is-sidebar-collapsed .search-label {
    display: block;
  }

  .app-shell.is-sidebar-collapsed .course-search {
    display: block;
  }

  .app-shell.is-sidebar-collapsed .tree-children.is-open {
    display: grid;
  }

  .app-shell.is-sidebar-collapsed .sidebar-toggle {
    position: static;
    width: 2rem;
    height: 2rem;
    margin-left: auto;
    transform: none;
  }

  .app-shell.is-sidebar-collapsed .course-tree {
    padding-top: 0;
  }

  .app-shell.is-sidebar-collapsed .tree-row {
    grid-template-columns: 1.05rem minmax(0, 1fr) auto;
    justify-items: stretch;
    min-height: 2.35rem;
    padding: 0.48rem 0.9rem;
  }

  .app-shell.is-sidebar-collapsed .tree-toggle {
    width: 1.05rem;
    height: 1.05rem;
    border-radius: 0;
    background: transparent;
  }

  .lesson-header,
  .lesson-details {
    grid-template-columns: 1fr;
  }

  .back-button {
    left: 0.85rem;
    bottom: calc(1.15rem + env(safe-area-inset-bottom, 0px));
  }

  .lesson-header {
    align-items: start;
  }

  .video-shell {
    width: min(100%, 46rem);
    min-height: auto;
    max-height: none;
  }

  .playlist-panel {
    display: none;
  }

  .playlist-panel[hidden] {
    display: none !important;
  }

  .mobile-lesson-progress {
    display: flex;
    align-items: center;
    gap: 0.6rem;
    margin: -0.1rem 0 0.65rem;
    color: var(--muted);
  }

  .mobile-progress-label {
    flex: 0 0 auto;
    font-size: 0.68rem;
    font-weight: 650;
    letter-spacing: 0.04em;
  }

  .mobile-progress-track {
    display: flex;
    align-items: center;
    gap: 0.22rem;
    width: min(9.5rem, 44vw);
  }

  .mobile-progress-mark {
    display: block;
    flex: 1 1 0;
    height: 0.22rem;
    border-radius: 999px;
    background: var(--line-strong);
  }

  .mobile-progress-mark[data-state="past"] {
    background: #777777;
  }

  .mobile-progress-mark[data-state="current"] {
    flex-grow: 1.8;
    background: var(--accent);
  }

  .mobile-module-panel {
    display: block;
    margin: 0 0 0.75rem;
  }

  .mobile-module-panel[hidden] {
    display: none !important;
  }

  .mobile-course-playlist {
    gap: 0.55rem;
    border: 1px solid var(--line);
    border-radius: 8px;
    background: var(--panel);
    padding: 0.72rem;
    box-shadow: var(--shadow);
  }

  .mobile-course-playlist .playlist-header {
    grid-template-columns: minmax(0, 1fr) auto auto;
    gap: 0.55rem;
    align-items: center;
    padding-bottom: 0.58rem;
  }

  .mobile-course-playlist .playlist-count {
    padding: 0.28rem 0.44rem;
    font-size: 0.68rem;
  }

  .mobile-up-next {
    display: grid;
    gap: 0.35rem;
    border: 1px solid var(--line);
    border-radius: 8px;
    background: var(--panel-soft);
    padding: 0.58rem 0.65rem;
  }

  .mobile-up-next span {
    color: var(--muted);
    font-size: 0.62rem;
    font-weight: 650;
    letter-spacing: 0.08em;
    text-transform: uppercase;
  }

  .mobile-up-next button {
    border: 0;
    background: transparent;
    color: var(--ink-strong);
    padding: 0;
    text-align: left;
    cursor: pointer;
    font-size: 0.82rem;
    font-weight: 650;
    line-height: 1.28;
  }

  .mobile-up-next button:disabled {
    cursor: default;
    color: var(--muted);
  }

  .mobile-course-playlist .playlist-list {
    max-height: 14rem;
    overflow-y: auto;
    padding-right: 0.1rem;
  }

  .mobile-course-playlist .playlist-row {
    padding: 0.58rem 0.62rem;
  }

  .playlist-toggle {
    display: inline-flex;
    align-items: center;
    min-height: 1.9rem;
    border: 1px solid var(--line-strong);
    border-radius: 999px;
    background: var(--gray-button);
    color: var(--ink);
    padding: 0.28rem 0.55rem;
    cursor: pointer;
    font-size: 0.72rem;
    font-weight: 650;
  }

  .course-playlist.is-collapsed .playlist-summary,
  .course-playlist.is-collapsed .playlist-progress,
  .course-playlist.is-collapsed .mobile-up-next,
  .course-playlist.is-collapsed .playlist-list {
    display: none;
  }

  .app-shell[data-mode="hub"] .lesson-main {
    min-height: 100dvh;
  }

  .app-shell[data-mode="hub"] .skill-hub {
    min-height: calc(100dvh - 10rem);
  }

  .app-shell[data-mode="hub"] .skill-card {
    min-height: 5.5rem;
  }
}

@media (max-width: 560px) {
  .lesson-main {
    padding: 0.65rem;
    padding-bottom: 4.2rem;
  }

  h2 {
    font-size: 1.55rem;
    line-height: 1.08;
  }

  .brand-lockup {
    align-items: flex-start;
    padding: 0.85rem;
  }

  .brand-logo {
    width: 3.5rem;
    height: 3.5rem;
  }

  .theme-row,
  .progress-card {
    padding-right: 0.85rem;
    padding-left: 0.85rem;
  }

  .search-label {
    padding-right: 0.85rem;
    padding-left: 0.85rem;
  }

  .course-search {
    width: calc(100% - 1.7rem);
    margin-right: 0.85rem;
    margin-left: 0.85rem;
  }

  .lesson-hero,
  .course-playlist,
  .player-panel {
    margin-bottom: 0.65rem;
  }

  .lesson-hero {
    padding: 0.9rem;
  }

  .lesson-header {
    gap: 0.65rem;
  }

  .lesson-status {
    justify-self: start;
  }

  .hub-header {
    align-items: center;
    padding: 0.7rem 0.78rem;
  }

  .hub-title {
    font-size: 0.86rem;
  }

  .skill-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 0.48rem;
  }

  .skill-card {
    aspect-ratio: 1 / 0.86;
    min-height: 0;
    gap: 0.45rem;
    padding: 0.68rem;
  }

  .skill-card-title {
    font-size: 0.8rem;
    line-height: 1.18;
  }

  .skill-card-footer {
    font-size: 0.64rem;
    line-height: 1.1;
  }

  .player-panel {
    padding: 0.55rem;
  }

  .video-shell {
    width: min(100%, 22rem);
    min-height: auto;
    max-height: none;
    aspect-ratio: 9 / 16;
  }

  .lesson-actions {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .lesson-actions .button {
    width: auto;
    min-height: 2.2rem;
    padding-right: 0.5rem;
    padding-left: 0.5rem;
    font-size: 0.78rem;
  }

  .sidebar-actions .button {
    width: 100%;
  }

  .playlist-row {
    grid-template-columns: 1.9rem minmax(0, 1fr);
  }

  .playlist-row-status {
    grid-column: 2;
  }
}