:root {
  --font-base: 16pt;
  --font-medium: 22pt;
  --font-large: 28pt;
  --ink: #17191d;
  --muted: #596069;
  --paper: #f6f7f4;
  --surface: #ffffff;
  --line: #d6d9d2;
  --panel: #eef2ec;
  --fretboard: #4a352b;
  --fretboard-dark: #31251f;
  --fret: #c5b18a;
  --string: #d9dfe0;
  --root: #f7c948;
  --root-ink: #1c1710;
  --note: #76d4c3;
  --note-ink: #10201e;
  --focus: #2f6fed;
}

* {
  box-sizing: border-box;
}

html {
  min-height: 100%;
  font-size: var(--font-base);
}

body {
  min-height: 100%;
  margin: 0;
  background:
    linear-gradient(180deg, rgba(23, 25, 29, 0.06), transparent 280px),
    var(--paper);
  color: var(--ink);
  font-family: Arial, Helvetica, sans-serif;
  font-size: var(--font-base);
  letter-spacing: 0;
}

button,
input,
select,
textarea {
  font: inherit;
  letter-spacing: 0;
}

.app-shell {
  width: min(1480px, calc(100% - 32px));
  margin: 0 auto;
  padding: 28px 0;
}

.app-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-end;
  gap: 24px;
  padding: 0 0 24px;
}

.app-header h1 {
  margin: 0;
  font-size: var(--font-large);
  line-height: 1.05;
}

.app-header p,
.educational-note {
  max-width: 980px;
  margin: 12px 0 0;
  color: var(--muted);
  line-height: 1.45;
}

.controls {
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
  margin-bottom: 22px;
}

.control-group,
.theory-panel,
.fretboard-section {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.82);
  box-shadow: 0 18px 44px rgba(23, 25, 29, 0.08);
}

.control-group {
  padding: 16px;
}

.control-group h2,
.theory-panel h2 {
  margin: 0 0 14px;
  font-size: var(--font-medium);
  line-height: 1.12;
}

.button-grid {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.control-button {
  min-height: 48px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  color: var(--ink);
  cursor: pointer;
  padding: 8px 14px;
  transition: background-color 160ms ease, border-color 160ms ease, color 160ms ease, transform 160ms ease;
}

.note-grid .control-button {
  min-width: 58px;
}

.structure-grid .control-button,
.mode-grid .control-button {
  min-width: 150px;
}

.control-button:hover {
  border-color: #9aa39a;
  transform: translateY(-1px);
}

.control-button:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 2px;
}

.control-button.is-active {
  border-color: #1f2a24;
  background: #1f2a24;
  color: #f7fbf5;
}

.learning-area {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(280px, 300px);
  gap: 22px;
  align-items: stretch;
}

.fretboard-section {
  min-width: 0;
  padding: 16px;
}

.active-combination {
  margin-bottom: 14px;
  color: var(--ink);
  font-size: var(--font-medium);
  font-weight: 700;
  line-height: 1.18;
}

.fretboard-scroll {
  overflow-x: auto;
  padding-bottom: 8px;
}

.fretboard-shell {
  display: grid;
  grid-template-columns: 76px minmax(792px, 1fr);
  min-width: 868px;
}

.headstock {
  display: grid;
  grid-template-rows: 36px repeat(4, 72px);
  border-radius: 8px 0 0 8px;
  background:
    linear-gradient(90deg, rgba(255, 255, 255, 0.08), transparent),
    #2c2d2a;
  color: #f7fbf5;
  overflow: hidden;
}

.headstock strong {
  display: grid;
  place-items: center;
  border-top: 1px solid rgba(255, 255, 255, 0.14);
  font-size: var(--font-base);
}

.fretboard-body {
  min-width: 0;
}

.fret-numbers {
  display: grid;
  grid-template-columns: repeat(12, minmax(66px, 1fr));
  height: 36px;
  color: var(--muted);
}

.fret-numbers span {
  display: grid;
  place-items: center;
  font-size: var(--font-base);
}

.fretboard-grid {
  position: relative;
  display: grid;
  grid-template-columns: repeat(12, minmax(66px, 1fr));
  grid-template-rows: repeat(4, 72px);
  overflow: hidden;
  border: 2px solid var(--fretboard-dark);
  border-left: 0;
  border-radius: 0 8px 8px 0;
  background:
    linear-gradient(90deg, rgba(255, 255, 255, 0.12), transparent 30%, rgba(0, 0, 0, 0.1)),
    linear-gradient(180deg, #5b4335, var(--fretboard) 48%, #3c2c24);
}

.marker-layer {
  position: absolute;
  inset: 0;
  z-index: 1;
  display: grid;
  grid-template-columns: repeat(12, minmax(66px, 1fr));
  pointer-events: none;
}

.marker-layer > span {
  position: relative;
}

.single-marker i,
.double-marker i {
  position: absolute;
  left: 50%;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: rgba(246, 247, 244, 0.36);
  transform: translate(-50%, -50%);
}

.single-marker i {
  top: 50%;
}

.double-marker i:first-child {
  top: 36%;
}

.double-marker i:last-child {
  top: 64%;
}

.fret-cell {
  position: relative;
  z-index: 2;
  display: grid;
  place-items: center;
  min-width: 66px;
  border-left: 3px solid var(--fret);
}

.fret-cell.last-fret {
  border-right: 3px solid var(--fret);
}

.fret-cell::before {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  top: 50%;
  z-index: 2;
  height: 3px;
  background: linear-gradient(180deg, #fbffff, var(--string) 48%, #8f999a);
  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.5);
  transform: translateY(-50%);
}

.fret-cell.string-1::before {
  height: 2px;
}

.fret-cell.string-2::before {
  height: 3px;
}

.fret-cell.string-3::before {
  height: 4px;
}

.fret-cell.string-4::before {
  height: 5px;
}

.note-token {
  position: relative;
  z-index: 4;
  display: grid;
  place-items: center;
  width: 60px;
  height: 60px;
  border: 2px solid rgba(255, 255, 255, 0.8);
  border-radius: 50%;
  background: var(--note);
  color: var(--note-ink);
  font-weight: 700;
  line-height: 1;
  box-shadow: 0 10px 18px rgba(0, 0, 0, 0.28);
}

.note-token span {
  font-size: var(--font-base);
}

.note-token.is-root {
  width: 66px;
  height: 66px;
  border-color: #fff4bb;
  background: var(--root);
  color: var(--root-ink);
  box-shadow: 0 0 0 5px rgba(247, 201, 72, 0.3), 0 12px 22px rgba(0, 0, 0, 0.32);
}

.theory-panel {
  padding: 18px;
}

.theory-panel dl {
  display: grid;
  gap: 16px;
  margin: 0;
}

.theory-panel dt {
  margin-bottom: 4px;
  color: var(--muted);
  font-weight: 700;
}

.theory-panel dd {
  margin: 0;
  line-height: 1.45;
}

.educational-note {
  margin-top: 22px;
  padding-bottom: 10px;
}

@media (max-width: 980px) {
  .learning-area {
    grid-template-columns: 1fr;
  }

  .theory-panel {
    order: 2;
  }
}

@media (max-width: 620px) {
  .app-shell {
    width: min(100% - 20px, 1480px);
    padding: 18px 0;
  }

  .app-header {
    display: block;
  }

  .control-group,
  .theory-panel,
  .fretboard-section {
    padding: 12px;
  }

  .structure-grid .control-button,
  .mode-grid .control-button {
    flex: 1 1 100%;
  }

  .active-combination {
    overflow-wrap: anywhere;
  }

  .fretboard-shell {
    grid-template-columns: 64px minmax(792px, 1fr);
    min-width: 856px;
  }

  .headstock {
    grid-template-rows: 36px repeat(4, 68px);
  }

  .fretboard-grid {
    grid-template-rows: repeat(4, 68px);
  }

  .note-token {
    width: 60px;
    height: 60px;
  }

  .note-token.is-root {
    width: 66px;
    height: 66px;
  }
}