:root {
  --accent: #3b82f6;
  --accent-dark: #2563eb;
  --accent-light: #93c5fd;
  --bg-grad-top: #e6f2ff;
  --bg-grad-mid: #f5f9ff;
  --bg-grad-bottom: #ffffff;
  --card-bg: #ffffff;
  --text: #1e293b;
  --muted: #64748b;
  --border: #e2e8f0;
  --key-white: #ffffff;
  --key-white-hover: #f8fafc;
  --key-white-shadow: rgba(0, 0, 0, 0.1);
  --key-black: #1f2937;
  --key-black-hover: #374151;
  --key-black-shadow: rgba(0, 0, 0, 0.3);
  --active-white: linear-gradient(180deg, #bfdbfe 0%, #3b82f6 100%);
  --active-black: linear-gradient(180deg, #60a5fa 0%, #1d4ed8 100%);
  --mark-color: #f59e0b;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.06);
  --shadow-md: 0 4px 12px rgba(30, 64, 175, 0.08);
  --shadow-lg: 0 20px 45px rgba(30, 64, 175, 0.12);
  --radius: 12px;
}

[data-theme="dark"] {
  --bg-grad-top: #0b1220;
  --bg-grad-mid: #0f172a;
  --bg-grad-bottom: #111827;
  --card-bg: #1e293b;
  --text: #e2e8f0;
  --muted: #94a3b8;
  --border: #334155;
  --key-white: #f1f5f9;
  --key-white-hover: #e2e8f0;
  --key-white-shadow: rgba(0, 0, 0, 0.4);
  --key-black: #0f172a;
  --key-black-hover: #1e293b;
  --key-black-shadow: rgba(0, 0, 0, 0.6);
  --active-white: linear-gradient(180deg, #93c5fd 0%, #2563eb 100%);
  --active-black: linear-gradient(180deg, #60a5fa 0%, #1e40af 100%);
  --mark-color: #fbbf24;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 20px 45px rgba(0, 0, 0, 0.4);
}

* { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "PingFang SC", "Microsoft YaHei", sans-serif;
  color: var(--text);
  background: linear-gradient(to bottom, var(--bg-grad-top) 0%, var(--bg-grad-mid) 55%, var(--bg-grad-bottom) 100%);
  min-height: 100vh;
  transition: background 0.3s ease, color 0.3s ease;
}

.container { max-width: 1080px; margin: 0 auto; padding: 0 20px; }
.container-narrow { max-width: 760px; }
.hidden { display: none !important; }

/* ---------- Header ---------- */
.header {
  position: sticky; top: 0; z-index: 50;
  background: var(--card-bg);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
  transition: background 0.3s ease;
}
.header-inner { display: flex; align-items: center; justify-content: space-between; gap: 16px; height: 60px; }
.brand { display: flex; align-items: center; gap: 8px; text-decoration: none; color: var(--text); font-weight: 700; }
.brand-icon { width: 26px; height: 26px; color: var(--accent-dark); }
.brand-name { font-size: 1.25rem; letter-spacing: -0.02em; }
.nav { display: flex; gap: 20px; }
.nav a { color: var(--muted); text-decoration: none; font-size: 0.95rem; transition: color 0.2s; }
.nav a:hover { color: var(--accent-dark); }
.header-actions { display: flex; align-items: center; gap: 10px; }
.icon-btn {
  display: inline-flex; align-items: center; justify-content: center;
  width: 38px; height: 38px; border-radius: 10px; border: 1px solid var(--border);
  background: var(--card-bg); color: var(--text); cursor: pointer; transition: all 0.2s;
}
.icon-btn:hover { border-color: var(--accent); color: var(--accent-dark); }
.icon-btn svg { width: 18px; height: 18px; }
.icon-moon { display: none; }
[data-theme="dark"] .icon-sun { display: none; }
[data-theme="dark"] .icon-moon { display: block; }

.lang-select-wrap { position: relative; display: flex; align-items: center; }
.lang-select-wrap .globe { position: absolute; left: 10px; width: 16px; height: 16px; color: var(--muted); pointer-events: none; }
.lang-select-wrap select {
  appearance: none; -webkit-appearance: none;
  padding: 8px 30px 8px 32px; border-radius: 10px;
  border: 1px solid var(--border); background: var(--card-bg); color: var(--text);
  font-size: 0.9rem; cursor: pointer;
}
select:focus { outline: 2px solid var(--accent); outline-offset: 1px; }

/* ---------- Hero ---------- */
.hero { padding: 48px 0 64px; }
.hero-title { font-size: clamp(2rem, 5vw, 3.2rem); font-weight: 800; letter-spacing: -0.03em; text-align: center; color: var(--text); }
.hero-sub { text-align: center; color: var(--muted); max-width: 620px; margin: 14px auto 36px; font-size: 1.05rem; line-height: 1.6; }

/* ---------- Piano card ---------- */
.piano-card {
  position: relative;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 18px;
  box-shadow: var(--shadow-lg);
  padding: 16px;
  transition: background 0.3s ease;
}
.loading-badge {
  position: absolute; top: 18px; right: 18px; z-index: 5;
  display: inline-flex; align-items: center; gap: 7px;
  font-size: 0.78rem; color: var(--muted);
  background: var(--card-bg); border: 1px solid var(--border);
  padding: 4px 10px; border-radius: 999px;
}
.loading-badge .dot { width: 7px; height: 7px; border-radius: 50%; background: var(--accent); animation: pulse 1.2s infinite; }
@keyframes pulse { 0%, 100% { opacity: 1; } 50% { opacity: 0.25; } }
.loading-badge.ready { display: none; }

.lesson-bar {
  display: flex; align-items: center; gap: 10px; flex-wrap: wrap;
  padding: 10px 12px; margin-bottom: 10px;
  background: linear-gradient(120deg, #eff6ff, #dbeafe);
  border: 1px solid var(--border); border-radius: var(--radius);
  font-size: 0.9rem;
}
[data-theme="dark"] .lesson-bar { background: linear-gradient(120deg, #1e293b, #24344d); }
.lesson-label { font-weight: 600; color: var(--accent-dark); }
.lesson-bar select, .toolbar select {
  padding: 6px 10px; border-radius: 8px; border: 1px solid var(--border);
  background: var(--card-bg); color: var(--text); font-size: 0.88rem;
}

.toolbar {
  display: flex; align-items: center; justify-content: space-between; gap: 12px; flex-wrap: wrap;
  padding: 6px 2px 12px;
}
.toolbar-group { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; }

.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 6px;
  padding: 7px 14px; border-radius: 9px; border: 1px solid var(--border);
  background: var(--card-bg); color: var(--text); font-size: 0.88rem; font-weight: 500;
  cursor: pointer; transition: all 0.15s ease; white-space: nowrap;
}
.btn:hover:not(:disabled) { border-color: var(--accent); color: var(--accent-dark); }
.btn:disabled { opacity: 0.45; cursor: not-allowed; }
.btn.active { background: var(--accent); border-color: var(--accent); color: #fff; box-shadow: var(--shadow-md); }
.btn-accent { background: var(--accent); border-color: var(--accent); color: #fff; }
.btn-accent:hover:not(:disabled) { background: var(--accent-dark); border-color: var(--accent-dark); color: #fff; }
.btn-small { padding: 4px 10px; font-size: 0.8rem; }
.btn-lg { padding: 12px 28px; font-size: 1rem; }
.btn-record { background: #111; border-color: #111; color: #fff; }
.btn-record:hover:not(:disabled) { background: #000; color: #fff; }
.btn-record.recording { background: #dc2626; border-color: #dc2626; }
.btn-download { background: #10b981; border-color: #10b981; color: #fff; }
.btn-download:hover:not(:disabled) { background: #059669; color: #fff; }

.toolbar-controls { gap: 16px; }
.ctrl { display: flex; align-items: center; gap: 8px; }
.ctrl-label { font-size: 0.8rem; color: var(--muted); }
.bpm-val { min-width: 36px; text-align: center; font-variant-numeric: tabular-nums; font-size: 0.9rem; color: var(--accent-dark); font-weight: 600; }
input[type="range"] { width: 110px; accent-color: var(--accent); cursor: pointer; }

/* ---------- Keyboard ---------- */
.keyboard {
  position: relative;
  display: flex;
  border-radius: 12px;
  overflow: hidden;
  overflow-x: auto;
  border: 1px solid var(--border);
  background: var(--card-bg);
  user-select: none;
  -webkit-user-select: none;
  padding: 4px;
}
.octave { position: relative; display: flex; flex: 1; min-width: 0; }
.key { position: relative; border: none; cursor: pointer; -webkit-tap-highlight-color: transparent; outline: none; }
.key:focus-visible { box-shadow: inset 0 0 0 2px var(--accent); }

.key.white {
  flex: 1;
  height: 190px;
  background: var(--key-white);
  border: 1px solid var(--border);
  border-top: none;
  border-radius: 0 0 6px 6px;
  box-shadow: inset 0 -6px 0 var(--key-white-shadow);
  transition: background 0.08s ease;
}
.key.white:hover { background: var(--key-white-hover); }
.key.white.active {
  background: var(--active-white);
  box-shadow: inset 0 -6px 0 rgba(0, 0, 0, 0.18);
  transform: translateY(2px);
}
.key.white.marked::after {
  content: ""; position: absolute; bottom: 8px; left: 50%; transform: translateX(-50%);
  width: 14px; height: 14px; border-radius: 50%; background: var(--mark-color);
}

.key.black {
  position: absolute; top: 0; z-index: 10;
  width: 8.7%;
  height: 120px;
  background: var(--key-black);
  border-radius: 0 0 5px 5px;
  box-shadow: inset 0 -6px 0 var(--key-black-shadow);
  transition: background 0.08s ease;
}
.key.black:hover { background: var(--key-black-hover); }
.key.black.active { background: var(--active-black); transform: translateY(2px); box-shadow: inset 0 -4px 0 rgba(0, 0, 0, 0.25); }
.key.black.marked::after {
  content: ""; position: absolute; bottom: 6px; left: 50%; transform: translateX(-50%);
  width: 10px; height: 10px; border-radius: 50%; background: var(--mark-color);
}
.key.white.pending { background: var(--active-white); }
.key.black.pending { background: var(--active-black); }

.kbd-label {
  position: absolute; top: 6px; left: 50%; transform: translateX(-50%);
  font-size: 0.7rem; color: #94a3b8; pointer-events: none; font-weight: 600;
}
.key.black .kbd-label { color: #9ca3af; }
.note-label {
  position: absolute; bottom: 8px; left: 50%; transform: translateX(-50%);
  font-size: 0.85rem; color: #94a3b8; pointer-events: none; font-weight: 600;
}
.key.black .note-label { color: #d1d5db; font-size: 0.72rem; bottom: 6px; }
.hide-notes .note-label { display: none; }

.key-hint { text-align: center; color: var(--muted); font-size: 0.82rem; margin: 14px 6px 4px; }

/* ---------- Panels ---------- */
.panels { display: flex; gap: 14px; flex-wrap: wrap; margin-top: 14px; }
.panel {
  flex: 1; min-width: 280px;
  border: 1px solid var(--border); border-radius: var(--radius);
  background: var(--card-bg); padding: 14px;
}
.panel-head { display: flex; align-items: center; justify-content: space-between; gap: 10px; margin-bottom: 10px; }
.panel-head h2 { font-size: 1rem; color: var(--text); }
.timer { font-variant-numeric: tabular-nums; font-size: 1rem; color: var(--accent-dark); font-weight: 600; }
.note-log-list {
  list-style: none; display: flex; flex-wrap: wrap; gap: 6px; max-height: 130px; overflow-y: auto;
}
.note-log-list li {
  font-size: 0.78rem; font-weight: 600; color: var(--accent-dark);
  background: #eff6ff; border: 1px solid #dbeafe; padding: 3px 8px; border-radius: 6px;
  font-variant-numeric: tabular-nums;
}
[data-theme="dark"] .note-log-list li { background: #1e3a5f; border-color: #1e3a5f; color: #bfdbfe; }
.empty { color: var(--muted); font-size: 0.88rem; }
.rec-body { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.rec-status { flex-basis: 100%; color: var(--muted); font-size: 0.85rem; margin-top: 4px; }

.piano-card-footer {
  display: flex; align-items: center; justify-content: space-between;
  padding: 14px 6px 2px; font-size: 0.85rem;
}
.card-brand { font-weight: 700; color: var(--accent-dark); }
.card-credit { color: var(--muted); }

/* ---------- Try button ---------- */
.try-btn {
  display: block; margin: 28px auto 0; text-align: center; width: max-content;
  padding: 12px 30px; border-radius: 999px;
  background: var(--accent); color: #fff; text-decoration: none; font-weight: 600;
  box-shadow: var(--shadow-md); transition: all 0.2s;
}
.try-btn:hover { background: var(--accent-dark); transform: translateY(-1px); }

/* ---------- Sections ---------- */
.section { padding: 64px 0; }
.section-alt { background: var(--card-bg); border-top: 1px solid var(--border); border-bottom: 1px solid var(--border); }
.section-title { text-align: center; font-size: clamp(1.5rem, 3vw, 2rem); font-weight: 800; letter-spacing: -0.02em; margin-bottom: 36px; }
.grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); gap: 18px; }
.card {
  background: var(--card-bg); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 22px; box-shadow: var(--shadow-sm);
}
.card h3 { font-size: 1.05rem; margin: 12px 0 8px; }
.card p { color: var(--muted); font-size: 0.92rem; line-height: 1.55; }
.icon-chip {
  width: 44px; height: 44px; border-radius: 12px;
  background: var(--accent); color: #fff;
  display: inline-flex; align-items: center; justify-content: center;
  background: linear-gradient(135deg, #60a5fa, #2563eb);
  box-shadow: var(--shadow-md);
}
.icon-chip svg { width: 22px; height: 22px; }

.steps { max-width: 720px; margin: 0 auto; padding-left: 22px; display: grid; gap: 12px; }
.steps li { color: var(--text); font-size: 1rem; line-height: 1.6; }

.faq { display: grid; gap: 12px; }
.faq details {
  background: var(--card-bg); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 16px 18px;
}
.faq summary { cursor: pointer; font-weight: 600; font-size: 1rem; }
.faq p { color: var(--muted); margin-top: 10px; line-height: 1.6; font-size: 0.95rem; }

.cta-band {
  background: linear-gradient(120deg, #1e3a8a, #1d4ed8);
  padding: 56px 20px; text-align: center; color: #fff;
  position: relative; overflow: hidden;
}
.cta-band h2 { font-size: 2rem; font-weight: 800; }
.cta-band p { margin: 10px auto 22px; max-width: 480px; color: #bfdbfe; }
.cta-band .btn-accent { background: #fff; border-color: #fff; color: #1d4ed8; }
.cta-band .btn-accent:hover { background: #e0f2fe; color: #1e3a8a; }

/* ---------- Footer ---------- */
.footer { background: var(--card-bg); border-top: 1px solid var(--border); padding-top: 40px; }
.footer-inner { display: flex; justify-content: space-between; gap: 24px; flex-wrap: wrap; padding-bottom: 24px; }
.footer-brand { font-weight: 800; font-size: 1.1rem; color: var(--accent-dark); }
.footer-tagline { color: var(--muted); font-size: 0.9rem; margin-top: 6px; max-width: 340px; }
.footer-nav { display: flex; gap: 20px; flex-wrap: wrap; }
.footer-nav a { color: var(--muted); text-decoration: none; font-size: 0.92rem; }
.footer-nav a:hover { color: var(--accent-dark); }
.footer-bottom { padding: 16px 0; border-top: 1px solid var(--border); color: var(--muted); font-size: 0.82rem; text-align: center; }

/* ---------- Toast ---------- */
.toast {
  position: fixed; left: 50%; bottom: 28px; transform: translateX(-50%) translateY(20px);
  background: #111827; color: #fff; padding: 10px 18px; border-radius: 999px;
  font-size: 0.88rem; box-shadow: var(--shadow-lg); opacity: 0; pointer-events: none;
  transition: all 0.25s ease; z-index: 100;
}
.toast.show { opacity: 1; transform: translateX(-50%) translateY(0); }

/* ---------- Responsive ---------- */
@media (max-width: 860px) {
  .nav { display: none; }
  .toolbar { justify-content: center; }
  .piano-card { padding: 12px; }
  .key.white { height: 150px; }
  .key.black { height: 96px; }
  .hero { padding: 28px 0 40px; }
}