/* ============================================
   Karplus-Strong Synthesizer - Main Stylesheet
   ============================================ */

/* ---------- Reset & Variables ---------- */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
    --c-bg: #0f1117;
    --c-surface: #1a1d27;
    --c-surface2: #242736;
    --c-border: #2e3245;
    --c-text: #e8eaf0;
    --c-text-dim: #8b90a5;
    --c-accent: #7c5cfc;
    --c-accent-glow: rgba(124, 92, 252, 0.25);
    --c-accent2: #00d4aa;
    --c-accent2-glow: rgba(0, 212, 170, 0.2);
    --c-danger: #ff5c5c;
    --c-warn: #ffc107;
    --font: 'Inter', system-ui, -apple-system, sans-serif;
    --radius: 10px;
    --radius-sm: 6px;
    --shadow: 0 4px 24px rgba(0,0,0,.35);
}

html { scroll-behavior: smooth; }

body {
    font-family: var(--font);
    background: var(--c-bg);
    color: var(--c-text);
    line-height: 1.7;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

a { color: var(--c-accent); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ---------- Navbar ---------- */
.navbar {
    background: var(--c-surface);
    border-bottom: 1px solid var(--c-border);
    position: sticky;
    top: 0;
    z-index: 100;
    backdrop-filter: blur(12px);
}
.nav-container {
    max-width: 1100px;
    margin: 0 auto;
    padding: .75rem 1.5rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
}
.nav-brand {
    font-size: 1.15rem;
    font-weight: 700;
    color: var(--c-accent);
    letter-spacing: -0.02em;
}
.nav-brand:hover { text-decoration: none; }
.nav-links { display: flex; align-items: center; gap: 1.25rem; }
.nav-links a {
    color: var(--c-text-dim);
    font-size: .9rem;
    font-weight: 500;
    transition: color .2s;
}
.nav-links a:hover { color: var(--c-text); text-decoration: none; }
.lang-toggle {
    background: var(--c-surface2);
    border: 1px solid var(--c-border);
    color: var(--c-text);
    padding: .3rem .65rem;
    border-radius: var(--radius-sm);
    font-size: .8rem;
    font-weight: 600;
    cursor: pointer;
    transition: all .2s;
}
.lang-toggle:hover {
    border-color: var(--c-accent);
    background: var(--c-accent-glow);
}

/* ---------- Main Content ---------- */
.main-content { flex: 1; }

/* ---------- Footer ---------- */
.footer {
    text-align: center;
    padding: 2rem 1.5rem;
    color: var(--c-text-dim);
    font-size: .82rem;
    border-top: 1px solid var(--c-border);
    margin-top: 3rem;
}
.footer-sub { font-size: .75rem; margin-top: .3rem; opacity: .65; }

/* ---------- Buttons ---------- */
.btn {
    display: inline-flex;
    align-items: center;
    gap: .45rem;
    padding: .55rem 1.25rem;
    border-radius: var(--radius-sm);
    font-size: .88rem;
    font-weight: 600;
    font-family: var(--font);
    cursor: pointer;
    border: none;
    transition: all .2s;
}
.btn-primary {
    background: var(--c-accent);
    color: #fff;
    box-shadow: 0 2px 12px var(--c-accent-glow);
}
.btn-primary:hover { filter: brightness(1.15); transform: translateY(-1px); }
.btn-secondary {
    background: var(--c-surface2);
    color: var(--c-text);
    border: 1px solid var(--c-border);
}
.btn-secondary:hover { border-color: var(--c-accent); background: var(--c-accent-glow); }
.btn-sm { padding: .4rem .9rem; font-size: .8rem; }
.btn-accent2 {
    background: var(--c-accent2);
    color: #0f1117;
    box-shadow: 0 2px 12px var(--c-accent2-glow);
}
.btn-accent2:hover { filter: brightness(1.15); }

/* ---------- HOME PAGE ---------- */
.hero {
    text-align: center;
    padding: 5rem 1.5rem 3rem;
    background: linear-gradient(180deg, var(--c-surface) 0%, var(--c-bg) 100%);
}
.hero h1 {
    font-size: 2.6rem;
    font-weight: 800;
    letter-spacing: -0.03em;
    background: linear-gradient(135deg, var(--c-accent), var(--c-accent2));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}
.hero .sub {
    color: var(--c-text-dim);
    max-width: 560px;
    margin: 1rem auto 2rem;
    font-size: 1.05rem;
}
.hero-buttons { display: flex; gap: 1rem; justify-content: center; flex-wrap: wrap; }

.features {
    max-width: 1000px;
    margin: 0 auto;
    padding: 3rem 1.5rem;
}
.features h2 { text-align: center; font-size: 1.6rem; margin-bottom: 2rem; }
.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.25rem;
}
.feature-card {
    background: var(--c-surface);
    border: 1px solid var(--c-border);
    border-radius: var(--radius);
    padding: 1.5rem;
    transition: border-color .3s, transform .2s;
}
.feature-card:hover { border-color: var(--c-accent); transform: translateY(-3px); }
.feature-card h3 { font-size: 1.05rem; margin-bottom: .5rem; color: var(--c-accent); }
.feature-card p { color: var(--c-text-dim); font-size: .9rem; }

.what-is {
    max-width: 750px;
    margin: 2rem auto 0;
    padding: 2.5rem 1.5rem;
}
.what-is h2 { font-size: 1.5rem; margin-bottom: 1rem; }
.what-is p { color: var(--c-text-dim); margin-bottom: 1rem; font-size: .95rem; }

/* ---------- LEARN PAGE ---------- */
.learn-page {
    max-width: 850px;
    margin: 0 auto;
    padding: 2rem 1.5rem 4rem;
}
.learn-page h1 {
    font-size: 2rem;
    font-weight: 800;
    margin-bottom: .5rem;
}
.learn-page .intro {
    color: var(--c-text-dim);
    font-size: 1.05rem;
    margin-bottom: 2rem;
}

/* Table of contents */
.toc {
    background: var(--c-surface);
    border: 1px solid var(--c-border);
    border-radius: var(--radius);
    padding: 1.25rem 1.5rem;
    margin-bottom: 3rem;
}
.toc h3 { font-size: .95rem; color: var(--c-text-dim); margin-bottom: .75rem; text-transform: uppercase; letter-spacing: .08em; }
.toc ul { list-style: none; }
.toc li { margin-bottom: .4rem; }
.toc a { color: var(--c-accent); font-weight: 500; font-size: .95rem; }

/* Learn sections */
.learn-section {
    margin-bottom: 4rem;
    scroll-margin-top: 5rem;
}
.learn-section h2 {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: 1rem;
    padding-bottom: .5rem;
    border-bottom: 2px solid var(--c-accent-glow);
}
.learn-section p {
    color: var(--c-text-dim);
    margin-bottom: 1rem;
    font-size: .95rem;
}

/* Steps cards */
.steps {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1rem;
    margin: 1.5rem 0;
}
.step-card {
    background: var(--c-surface);
    border: 1px solid var(--c-border);
    border-radius: var(--radius);
    padding: 1.25rem;
    text-align: center;
}
.step-card .step-num {
    display: inline-block;
    width: 2.2rem;
    height: 2.2rem;
    line-height: 2.2rem;
    background: var(--c-accent);
    color: #fff;
    border-radius: 50%;
    font-weight: 700;
    font-size: .9rem;
    margin-bottom: .5rem;
}
.step-card h4 { font-size: .95rem; margin-bottom: .3rem; }
.step-card p { font-size: .85rem; color: var(--c-text-dim); }

/* Demo boxes */
.demo-box {
    background: var(--c-surface);
    border: 1px solid var(--c-border);
    border-radius: var(--radius);
    padding: 1.5rem;
    margin: 1.5rem 0;
}
.demo-box canvas {
    width: 100%;
    height: 180px;
    border-radius: var(--radius-sm);
    background: #13151f;
    display: block;
    margin-bottom: 1rem;
}
.demo-controls {
    display: flex;
    align-items: center;
    gap: 1rem;
    flex-wrap: wrap;
    margin-top: .75rem;
}
.demo-controls label {
    font-size: .85rem;
    font-weight: 500;
    color: var(--c-text-dim);
    display: flex;
    align-items: center;
    gap: .5rem;
}
.demo-controls input[type="range"] {
    width: 180px;
    accent-color: var(--c-accent);
}
.demo-controls .value-display {
    background: var(--c-surface2);
    padding: .15rem .5rem;
    border-radius: var(--radius-sm);
    font-size: .8rem;
    font-weight: 600;
    min-width: 50px;
    text-align: center;
}

/* Math formula box */
.formula-box {
    background: var(--c-surface2);
    border-left: 3px solid var(--c-accent);
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
    padding: 1rem 1.25rem;
    margin: 1.25rem 0;
    font-size: .95rem;
    overflow-x: auto;
}
.formula-box .katex { font-size: 1.2em; }

/* Preset cards for Section 5 */
.preset-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
    gap: .75rem;
    margin: 1.25rem 0 2rem;
}
.preset-card {
    background: var(--c-surface2);
    border: 2px solid var(--c-border);
    border-radius: var(--radius-sm);
    padding: .85rem;
    cursor: pointer;
    transition: all .2s;
    text-align: center;
}
.preset-card:hover {
    border-color: var(--c-accent2);
    background: rgba(0, 212, 170, 0.08);
    transform: translateY(-2px);
}
.preset-card h4 {
    font-size: .9rem;
    font-weight: 600;
    color: var(--c-accent2);
    margin-bottom: .25rem;
}
.preset-card p {
    font-size: .75rem;
    color: var(--c-text-dim);
    margin: 0;
}

/* ---------- NEW: Advanced Learn Components ---------- */

/* Taller canvas for spectrum visualization (waveform + spectrum stacked) */
.demo-box canvas.tall {
    height: 320px;
}

/* Circular buffer visualization */
.ring-buffer-vis {
    position: relative;
    width: 100%;
    height: 280px;
}

/* Comparison panels (side-by-side or stacked demos) */
.comparison-panel {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 1rem;
    margin: 1.5rem 0;
}

.comparison-item {
    background: var(--c-surface2);
    border: 1px solid var(--c-border);
    border-radius: var(--radius-sm);
    padding: 1rem;
}

.comparison-item h4 {
    font-size: .9rem;
    color: var(--c-accent);
    margin-bottom: .5rem;
}

.comparison-item canvas {
    width: 100%;
    height: 140px;
    border-radius: var(--radius-sm);
    background: #13151f;
    display: block;
    margin-bottom: .5rem;
}

/* Milestone marks for filter slider */
.slider-with-marks {
    position: relative;
    width: 100%;
}

.slider-marks {
    display: flex;
    justify-content: space-between;
    margin-top: .25rem;
    font-size: .7rem;
    color: var(--c-text-dim);
    pointer-events: none;
}

.slider-mark {
    flex-shrink: 0;
    text-align: center;
}

/* Advanced parameters grid */
.param-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.25rem;
    margin: 1.5rem 0;
}

.param-card {
    background: var(--c-surface2);
    border: 1px solid var(--c-border);
    border-radius: var(--radius-sm);
    padding: 1.25rem;
}

.param-card h4 {
    font-size: .95rem;
    color: var(--c-accent2);
    margin-bottom: .75rem;
    display: flex;
    align-items: center;
    gap: .5rem;
}

.param-card p {
    font-size: .85rem;
    color: var(--c-text-dim);
    margin-bottom: .75rem;
}

.param-controls {
    display: flex;
    flex-direction: column;
    gap: .5rem;
}

.param-controls label {
    font-size: .82rem;
    color: var(--c-text);
    display: flex;
    align-items: center;
    gap: .5rem;
}

.param-controls input[type="range"] {
    flex: 1;
    accent-color: var(--c-accent2);
}

/* Spectrum display styling */
.spectrum-display {
    background: #0a0c10;
    border-radius: var(--radius-sm);
    padding: .5rem;
}

.spectrum-label {
    font-size: .75rem;
    color: var(--c-text-dim);
    text-transform: uppercase;
    margin-bottom: .35rem;
    letter-spacing: .05em;
}

/* Transition text styling */
.transition-text {
    background: var(--c-surface2);
    border-left: 3px solid var(--c-accent2);
    padding: .85rem 1rem;
    margin: 1.5rem 0;
    font-style: italic;
    color: var(--c-text-dim);
    font-size: .9rem;
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}

/* AB comparison toggle */
.ab-toggle {
    display: inline-flex;
    background: var(--c-surface2);
    border-radius: var(--radius-sm);
    padding: .25rem;
    gap: .25rem;
}

.ab-toggle button {
    padding: .4rem .9rem;
    background: transparent;
    border: none;
    border-radius: var(--radius-sm);
    font-size: .8rem;
    color: var(--c-text-dim);
    cursor: pointer;
    transition: all .2s;
}

.ab-toggle button.active {
    background: var(--c-accent);
    color: #fff;
}

.ab-toggle button:hover:not(.active) {
    background: rgba(255, 255, 255, 0.05);
}

/* Block diagram for section 1 */
.block-diagram {
    background: var(--c-surface2);
    border: 1px solid var(--c-border);
    border-radius: var(--radius);
    padding: 1.5rem;
    margin: 1.5rem 0;
    overflow-x: auto;
}

.diagram-flow {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 1rem;
    min-width: 600px;
}

.diagram-block {
    background: var(--c-surface);
    border: 2px solid var(--c-accent);
    border-radius: var(--radius-sm);
    padding: .75rem 1rem;
    text-align: center;
    min-width: 100px;
}

.diagram-block-title {
    font-size: .8rem;
    font-weight: 600;
    color: var(--c-accent);
    margin-bottom: .25rem;
}

.diagram-block-desc {
    font-size: .7rem;
    color: var(--c-text-dim);
}

.diagram-arrow {
    font-size: 1.5rem;
    color: var(--c-accent2);
}

/* Info callout boxes */
.info-box {
    background: rgba(124, 92, 252, 0.1);
    border: 1px solid var(--c-accent-glow);
    border-radius: var(--radius-sm);
    padding: 1rem;
    margin: 1rem 0;
}

.info-box.tip {
    background: rgba(0, 212, 170, 0.1);
    border-color: var(--c-accent2-glow);
}

.info-box.warning {
    background: rgba(255, 193, 7, 0.1);
    border-color: rgba(255, 193, 7, 0.3);
}

.info-box-title {
    font-size: .85rem;
    font-weight: 600;
    margin-bottom: .5rem;
    display: flex;
    align-items: center;
    gap: .5rem;
}

.info-box-content {
    font-size: .85rem;
    color: var(--c-text-dim);
}


/* ---------- COMPOSE PAGE ---------- */
.compose-page {
    max-width: 1050px;
    margin: 0 auto;
    padding: 2rem 1.5rem 4rem;
}
.compose-page h1 {
    font-size: 1.8rem;
    font-weight: 700;
    margin-bottom: .5rem;
}
.compose-page .desc {
    color: var(--c-text-dim);
    margin-bottom: 1.5rem;
    font-size: .95rem;
}
.compose-toolbar {
    display: flex;
    align-items: stretch;
    gap: 0;
    flex-wrap: wrap;
    margin-bottom: 1rem;
    padding: .5rem;
    background: var(--c-surface);
    border: 1px solid var(--c-border);
    border-radius: var(--radius);
}
.toolbar-group {
    display: flex;
    flex-direction: column;
    gap: .35rem;
    padding: .4rem .75rem;
    flex-shrink: 0;
}
.toolbar-group-label {
    font-size: .65rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: .08em;
    color: var(--c-text-dim);
    opacity: .7;
}
.toolbar-group-controls {
    display: flex;
    align-items: center;
    gap: .6rem;
    flex-wrap: wrap;
}
.toolbar-separator {
    width: 1px;
    background: var(--c-border);
    align-self: stretch;
    margin: .25rem 0;
}
.compose-toolbar label {
    font-size: .82rem;
    color: var(--c-text-dim);
    font-weight: 500;
    display: flex;
    align-items: center;
    gap: .4rem;
}
.compose-toolbar input[type="range"] { width: 100px; accent-color: var(--c-accent); }
.compose-toolbar select {
    background: var(--c-surface2);
    color: var(--c-text);
    border: 1px solid var(--c-border);
    padding: .3rem .5rem;
    border-radius: var(--radius-sm);
    font-size: .82rem;
    font-family: var(--font);
}

/* Playback indicator (pulsing dot) */
.playback-indicator {
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background: var(--c-text-dim);
    opacity: .3;
    transition: all .2s;
}
.playback-indicator.active {
    background: var(--c-danger);
    opacity: 1;
    animation: pulse-dot 1s ease-in-out infinite;
}
@keyframes pulse-dot {
    0%, 100% { transform: scale(1); opacity: 1; }
    50% { transform: scale(1.4); opacity: .7; }
}

/* Waveform Visualization Panel */
.waveform-panel {
    background: var(--c-surface);
    border: 1px solid var(--c-border);
    border-radius: var(--radius);
    margin-bottom: 1.5rem;
    overflow: hidden;
}
.waveform-panel-header {
    display: flex;
    align-items: center;
    padding: .75rem 1rem;
    border-bottom: 1px solid var(--c-border);
}
.waveform-panel-header h3 {
    font-size: .9rem;
    font-weight: 600;
    color: var(--c-text);
}
.waveform-panel-body {
    padding: 1rem;
}
.waveform-stage {
    margin-bottom: .75rem;
}
.waveform-stage:last-child {
    margin-bottom: 0;
}
.waveform-stage-label {
    display: block;
    font-size: .75rem;
    font-weight: 600;
    color: var(--c-text-dim);
    margin-bottom: .35rem;
    text-transform: uppercase;
    letter-spacing: .04em;
}
.waveform-stage canvas {
    width: 100%;
    height: 80px;
    border-radius: var(--radius-sm);
    background: #13151f;
    display: block;
}
.waveform-mix-container {
    position: relative;
}
.waveform-mix-container canvas#wfMix {
    width: 100%;
    height: 120px;
    border-radius: var(--radius-sm);
    background: #13151f;
    display: block;
}
.waveform-playhead-overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 120px;
    pointer-events: none;
}

.piano-roll-wrapper {
    background: var(--c-surface);
    border: 1px solid var(--c-border);
    border-radius: var(--radius);
    overflow: hidden;
    margin-bottom: 1.5rem;
}
.piano-roll-wrapper canvas {
    display: block;
    width: 100%;
    height: 400px;
}

.compose-tips {
    background: var(--c-surface);
    border: 1px solid var(--c-border);
    border-radius: var(--radius);
    padding: 1.25rem;
}
.compose-tips h3 { font-size: .95rem; margin-bottom: .5rem; color: var(--c-accent); }
.compose-tips ul { list-style: disc; padding-left: 1.25rem; }
.compose-tips li { color: var(--c-text-dim); font-size: .85rem; margin-bottom: .3rem; }

/* ---------- Utilities ---------- */
.text-center { text-align: center; }
.mt-1 { margin-top: .5rem; }
.mt-2 { margin-top: 1rem; }
.mt-3 { margin-top: 1.5rem; }
.mb-2 { margin-bottom: 1rem; }

/* ---------- Responsive ---------- */
@media (max-width: 640px) {
    .hero h1 { font-size: 1.8rem; }
    .hero { padding: 3rem 1rem 2rem; }
    .learn-page { padding: 1.5rem 1rem 3rem; }
    .demo-controls { flex-direction: column; align-items: flex-start; }
    .demo-controls input[type="range"] { width: 100%; }
    .steps { grid-template-columns: 1fr; }
    .compose-toolbar { flex-direction: column; }
    .toolbar-separator { width: 100%; height: 1px; margin: 0 .25rem; }
    .toolbar-group { width: 100%; }
    .waveform-panel-header { flex-direction: column; gap: .5rem; align-items: flex-start; }
}