:root {
  --bg-primary: #0a0a0f;
  --bg-secondary: #14141f;
  --bg-tertiary: #1e1e2e;
  --text-primary: #ffffff;
  --text-secondary: #a0a0b0;
  --text-muted: #606070;
  --accent: #00d4ff;
  --accent-secondary: #00ff88;
  --danger: #ff4466;
  --focus-ring: #00d4ff;
  --focus-glow: rgba(0, 212, 255, 0.4);
  --radius-md: 12px;
}
* { margin: 0; padding: 0; box-sizing: border-box; }
html, body {
  width: 600px; height: 600px; overflow: hidden;
  background: #000;
  color: var(--text-primary);
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
}
#app { width: 100%; height: 100%; position: relative; }
.screen { width: 100%; height: 100%; position: absolute; top: 0; left: 0; display: flex; flex-direction: column; }
.screen.hidden { display: none; }
.focusable { transition: all 0.15s ease; border: 2px solid transparent; cursor: pointer; outline: none; }
.focusable:focus { border-color: var(--focus-ring); box-shadow: 0 0 20px var(--focus-glow); }
.hidden { display: none !important; }

/* ---------- HOME ---------- */
.home-head {
  padding: 40px 32px 24px;
  text-align: center;
}
.home-logo { font-size: 56px; line-height: 1; margin-bottom: 8px; }
.home-head h1 { font-size: 36px; font-weight: 700; letter-spacing: 0.5px; }
.home-sub { color: var(--text-secondary); font-size: 16px; margin-top: 8px; letter-spacing: 2px; }

.menu {
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 14px;
  padding: 10px 32px 32px;
  justify-content: center;
}
.menu-tail { flex: 0; justify-content: flex-end; padding-bottom: 40px; }
.menu-btn {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  justify-content: center;
  min-height: 88px;
  padding: 14px 24px;
  border-radius: var(--radius-md);
  background: var(--bg-secondary);
  color: var(--text-primary);
  text-align: left;
  width: 100%;
  position: relative;
}
.mb-title { font-size: 24px; font-weight: 600; }
.mb-desc { font-size: 15px; color: var(--text-secondary); margin-top: 4px; }
.mb-val {
  position: absolute;
  right: 24px;
  top: 50%;
  transform: translateY(-50%);
  font-size: 22px;
  font-weight: 600;
  color: var(--accent);
}

/* ---------- SUB HEADERS ---------- */
.sub-head {
  padding: 28px 32px 12px;
  border-bottom: 1px solid var(--bg-tertiary);
  background: var(--bg-primary);
}
.sub-head h2 { font-size: 30px; font-weight: 700; }

/* ---------- HELP ---------- */
.help-body { flex: 1; padding: 20px 32px; overflow: hidden; }
.help-block { margin-bottom: 18px; }
.help-block h3 { font-size: 20px; color: var(--accent); margin-bottom: 6px; }
.help-block p { font-size: 17px; line-height: 1.45; color: var(--text-secondary); }
.help-block b { color: var(--text-primary); }

/* ---------- FRETBOARD ---------- */
.fb-header {
  height: 84px;
  padding: 10px 20px;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--bg-tertiary);
  position: relative;
}
.fb-mode {
  position: absolute;
  top: 10px; right: 18px;
  font-size: 13px;
  letter-spacing: 2px;
  text-transform: uppercase;
  color: var(--accent);
  font-weight: 600;
}
.fb-big { font-size: 32px; font-weight: 700; line-height: 1.2; }
.fb-sub { font-size: 15px; color: var(--text-secondary); margin-top: 4px; }

.fb-board {
  flex: 1;
  display: grid;
  grid-template-columns: 44px repeat(13, 1fr);
  grid-template-rows: 26px repeat(6, 1fr);
  background: var(--bg-primary);
  padding: 0 4px 4px;
}
.fb-corner { background: var(--bg-primary); }

.fb-fretnum {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 12px;
  color: var(--text-muted);
  position: relative;
}
.fb-fretnum.marker::after {
  content: '';
  position: absolute;
  bottom: -2px; left: 50%;
  transform: translateX(-50%);
  width: 5px; height: 5px;
  border-radius: 50%;
  background: var(--text-muted);
}
.fb-fretnum.marker-double::before,
.fb-fretnum.marker-double::after {
  content: '';
  position: absolute;
  bottom: -2px;
  width: 5px; height: 5px;
  border-radius: 50%;
  background: var(--accent);
}
.fb-fretnum.marker-double::before { left: calc(50% - 7px); }
.fb-fretnum.marker-double::after { left: calc(50% + 2px); }

.fb-strlabel {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  font-weight: 700;
  color: var(--text-secondary);
  box-shadow: inset -3px 0 0 var(--text-muted);
}
.fb-strlabel.target { color: var(--accent); background: rgba(0, 212, 255, 0.12); }

.fret-cell {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 15px;
  font-weight: 600;
  color: var(--text-primary);
  position: relative;
  box-shadow: inset -1px -1px 0 var(--bg-tertiary);
}
.fret-cell.open {
  box-shadow: inset -3px -1px 0 var(--text-muted);
  color: var(--accent);
}
.fret-cell:focus { z-index: 3; }
.fret-cell.selected { background: var(--accent); color: #001016; }
.fret-cell.correct { background: var(--accent-secondary); color: #001016; }
.fret-cell.wrong { background: var(--danger); color: #fff; }

.fb-board.hide-notes .cell-note { visibility: hidden; }
.fb-board.hide-notes .cell-note.revealed { visibility: visible; }

.fb-hint {
  height: 34px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 13px;
  letter-spacing: 1px;
  color: var(--text-muted);
  background: var(--bg-secondary);
  border-top: 1px solid var(--bg-tertiary);
}