/* ============================================================
   Đàn Piano Học Nhạc — giao diện
   Phong cách: nền sáng, thân đàn tím than để phím nổi bật
   ============================================================ */
:root {
  --bg:        #f3f0fb;
  --panel:     #ffffff;
  --line:      #e6e1f2;
  --ink:       #241f36;
  --ink-2:     #5f5878;
  --ink-3:     #8f88a6;

  --accent:    #7c3aed;   /* tím */
  --accent-d:  #6025d0;
  --accent-l:  #efe8fe;
  --body:      #2b2440;   /* thân đàn */
  --body-2:    #211b33;
  --danger:    #e5484d;

  --wkey: 48px;   /* bề rộng phím trắng */
  --bkey: 30px;   /* bề rộng phím đen */

  --font: "Nunito", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --shadow-sm: 0 1px 2px rgba(36,31,54,.06), 0 4px 16px rgba(36,31,54,.07);
}

* { margin: 0; padding: 0; box-sizing: border-box; }
html, body { height: 100%; }
body {
  font-family: var(--font);
  color: var(--ink);
  background:
    radial-gradient(1100px 480px at 84% -12%, #ece2ff 0%, transparent 58%),
    radial-gradient(900px 440px at -6% 0%, #e6ecff 0%, transparent 55%),
    var(--bg);
  display: flex; flex-direction: column;
  overflow: hidden;
  -webkit-font-smoothing: antialiased;
  touch-action: manipulation;
}

/* ---------- Thanh trên ---------- */
.bar {
  flex-shrink: 0;
  display: flex; align-items: center; gap: 12px;
  padding: 12px 16px 6px;
}
.back {
  display: inline-flex; align-items: center; gap: 6px;
  font-family: var(--font); font-size: 14px; font-weight: 800;
  color: var(--ink-2); background: var(--panel);
  border: 1px solid var(--line); border-radius: 999px;
  padding: 8px 14px 8px 11px; cursor: pointer; box-shadow: var(--shadow-sm);
  transition: color .15s, transform .05s;
}
.back:hover { color: var(--accent); }
.back:active { transform: scale(.97); }
.bar__title { font-size: clamp(1.1rem, 2.6vw, 1.4rem); font-weight: 900; color: var(--accent-d); }

/* ---------- Điều khiển ---------- */
.controls {
  flex-shrink: 0;
  display: flex; align-items: center; flex-wrap: wrap; gap: 10px 18px;
  padding: 10px 16px;
  margin: 6px 16px 0;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 16px;
  box-shadow: var(--shadow-sm);
}
.ctl { display: inline-flex; align-items: center; gap: 8px; }
.ctl__label { font-size: 12.5px; font-weight: 800; color: var(--ink-3); white-space: nowrap; }
#volume { width: 110px; accent-color: var(--accent); cursor: pointer; }

.select { position: relative; }
.select select {
  appearance: none; font-family: var(--font); font-size: 14px; font-weight: 800;
  color: var(--ink); background: var(--bg);
  border: 1.5px solid var(--line); border-radius: 9px;
  padding: 7px 30px 7px 12px; cursor: pointer;
}
.select__caret { position: absolute; right: 9px; top: 50%; transform: translateY(-50%); color: var(--ink-3); pointer-events: none; }

.chip {
  font-family: var(--font); font-size: 13.5px; font-weight: 800;
  color: #fff; background: var(--accent);
  border: none; border-radius: 999px; padding: 8px 16px; cursor: pointer;
  box-shadow: 0 3px 10px rgba(124,58,237,.32); transition: background .15s, transform .05s;
  min-width: 92px;
}
.chip:hover { background: var(--accent-d); }
.chip:active { transform: translateY(1px); }
.chip--song { background: #f59e0b; box-shadow: 0 3px 10px rgba(245,158,11,.32); min-width: 150px; }
.chip--song:hover { background: #e08800; }
.chip--song.is-playing { background: var(--danger); box-shadow: 0 3px 10px rgba(229,72,77,.32); }
.chip--song.is-playing:hover { background: #cf3b40; }

/* Phím đang được tự động chơi */
.key.white.demo { background: linear-gradient(180deg, #ffedb8 0%, #ffd873 100%); color: #7a4f00; }
.key.black.demo { background: linear-gradient(180deg, #f5a623 0%, #d98a00 100%); color: #fff; }

.bg-btns { display: inline-flex; gap: 5px; flex-wrap: wrap; }
.bgbtn {
  font-family: var(--font); font-size: 13px; font-weight: 800;
  color: var(--ink-2); background: var(--bg);
  border: 1.5px solid var(--line); border-radius: 8px;
  min-width: 34px; padding: 7px 10px; cursor: pointer;
  transition: all .15s;
}
.bgbtn:hover { border-color: var(--accent); color: var(--accent); }
.bgbtn.is-on { background: var(--accent); border-color: var(--accent); color: #fff; }
.bgbtn--stop { color: var(--danger); }
.bgbtn--stop:hover { background: #fdecec; border-color: var(--danger); color: var(--danger); }

/* ---------- Đàn ---------- */
.piano-wrap {
  flex: 1; min-height: 0;
  display: flex; align-items: center; justify-content: center;
  padding: 14px 16px;
  overflow-x: auto; overflow-y: hidden;
}
.piano {
  display: flex;
  height: 100%; max-height: 340px; min-height: 150px;
  padding: 12px 12px 14px;
  background: linear-gradient(180deg, var(--body) 0%, var(--body-2) 100%);
  border-radius: 14px;
  box-shadow: 0 12px 30px rgba(36,31,54,.28), inset 0 2px 0 rgba(255,255,255,.06);
}
.octave { position: relative; display: flex; }

.key {
  position: relative;
  cursor: pointer; user-select: none;
  display: flex; flex-direction: column; align-items: center; justify-content: flex-end;
  font-weight: 800;
  transition: background .06s, transform .04s;
}
.key .kb { font-size: 10px; font-weight: 800; opacity: .5; margin-bottom: auto; margin-top: 6px; }
.key .nm { line-height: 1.1; }
.key .oc { font-size: 9px; opacity: .55; font-weight: 700; }

.key.white {
  width: var(--wkey); height: 100%;
  background: linear-gradient(180deg, #ffffff 0%, #f1eef8 100%);
  color: #4a4360;
  border: 1px solid #d7d0e8;
  border-radius: 0 0 7px 7px;
  z-index: 1;
  padding-bottom: 10px; font-size: 12px;
}
.key.white + .key.white { margin-left: -1px; }
.key.white:active, .key.white.active {
  background: linear-gradient(180deg, var(--accent-l) 0%, #dcccfb 100%);
  color: var(--accent-d);
  transform: translateY(1px);
}

.key.black {
  position: absolute; top: 0;
  width: var(--bkey); height: 62%;
  background: linear-gradient(180deg, #3a3350 0%, #17131f 100%);
  color: #e7e2f3;
  border-radius: 0 0 6px 6px;
  z-index: 2;
  padding-bottom: 8px; font-size: 10px;
  box-shadow: 0 3px 6px rgba(0,0,0,.4);
}
.key.black .kb { opacity: .6; }
.key.black:active, .key.black.active {
  background: linear-gradient(180deg, var(--accent) 0%, var(--accent-d) 100%);
  color: #fff;
}

/* Vị trí phím đen theo bề rộng phím trắng */
.key.black.cs { left: calc(var(--wkey) * 1 - var(--bkey) / 2); }
.key.black.ds { left: calc(var(--wkey) * 2 - var(--bkey) / 2); }
.key.black.fs { left: calc(var(--wkey) * 4 - var(--bkey) / 2); }
.key.black.gs { left: calc(var(--wkey) * 5 - var(--bkey) / 2); }
.key.black.as { left: calc(var(--wkey) * 6 - var(--bkey) / 2); }

.hint {
  flex-shrink: 0;
  text-align: center; font-size: 12.5px; font-weight: 600; color: var(--ink-3);
  padding: 0 16px 12px;
}

/* ---------- Responsive ---------- */
@media (max-width: 900px) { :root { --wkey: 42px; --bkey: 26px; } }
@media (max-width: 640px) {
  :root { --wkey: 40px; --bkey: 25px; }
  .bar { padding: 8px 12px 4px; }
  .back__txt { display: none; }
  .controls { margin: 6px 10px 0; gap: 8px 12px; padding: 8px 12px; }
  .piano-wrap { padding: 10px; justify-content: flex-start; }
  .piano { max-height: none; }
  .hint { display: none; }
  .key .oc { display: none; }
}

@media (prefers-reduced-motion: reduce) { .key, .back, .chip, .bgbtn { transition: none; } }