/* StackBuilt — Design System */
:root {
    --bg-primary: #0a0a0f;
    --bg-secondary: #12121a;
    --bg-card: #1a1a24;
    --bg-card-hover: #222230;
    --bg-hover: #222230;
    --border: #2a2a3a;
    --text-primary: #ffffff;
    --text-secondary: #9ca3af;
    --text-muted: #6b7280;
    --accent: #6366f1;
    --accent-hover: #5558e8;
    --accent-glow: rgba(99,102,241,0.25);
    --accent-dim: rgba(99,102,241,0.12);
    --success: #22c55e;
    --warning: #f59e0b;
    --danger: #ef4444;
    --error: #ef4444;
    --radius: 12px;
    --radius-sm: 8px;
    --shadow: 0 4px 24px rgba(0,0,0,0.4);
    --mono: 'SF Mono','Fira Code','Fira Mono','Roboto Mono',monospace;
}

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

html { font-size: 16px; -webkit-font-smoothing: antialiased; }

body {
    font-family: -apple-system, BlinkMacSystemFont, 'SF Pro Display', 'Segoe UI', Roboto, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100vh;
    line-height: 1.6;
}

body::before {
    content: '';
    position: fixed;
    inset: 0;
    background:
        radial-gradient(ellipse at 20% 20%, rgba(99,102,241,0.07) 0%, transparent 50%),
        radial-gradient(ellipse at 80% 80%, rgba(139,92,246,0.05) 0%, transparent 50%);
    pointer-events: none;
    z-index: 0;
}

a { color: inherit; text-decoration: none; }
a:hover { text-decoration: none; }
button { font-family: inherit; }

/* ── Buttons ── */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    padding: 0.625rem 1.25rem;
    border-radius: var(--radius-sm);
    font-size: 0.875rem;
    font-weight: 600;
    cursor: pointer;
    border: none;
    font-family: inherit;
    transition: opacity 0.15s, transform 0.15s;
    text-decoration: none;
    line-height: 1;
}
.btn:hover { opacity: 0.88; transform: translateY(-1px); text-decoration: none; }
.btn-primary {
    background: var(--accent);
    color: #fff;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 0.7rem 1.4rem;
    border-radius: 10px;
    font-weight: 600;
    font-size: 0.95rem;
    cursor: pointer;
    text-decoration: none;
    border: none;
    transition: background 0.15s, transform 0.1s, opacity 0.15s;
    line-height: 1;
}
.btn-primary:hover { background: var(--accent-hover); opacity: 1; transform: none; text-decoration: none; }
.btn-primary:active { transform: scale(0.98); }
.btn-primary.btn-lg { padding: 0.9rem 1.8rem; font-size: 1rem; }
.btn-primary.btn-block { width: 100%; display: flex; }
.btn-outline {
    background: transparent;
    border: 1px solid var(--border);
    color: var(--text-secondary);
}
.btn-outline:hover { border-color: var(--accent); color: var(--text-primary); }
.btn-ghost {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    background: transparent;
    color: var(--text-primary);
    border: 1px solid var(--border);
    padding: 0.7rem 1.4rem;
    border-radius: 10px;
    font-weight: 500;
    font-size: 0.95rem;
    cursor: pointer;
    text-decoration: none;
    transition: border-color 0.15s, color 0.15s;
}
.btn-ghost:hover { border-color: var(--text-secondary); text-decoration: none; }
.btn-ghost.btn-lg { padding: 0.9rem 1.8rem; font-size: 1rem; }
.btn-ghost.btn-block { width: 100%; display: flex; }
.btn-lg { padding: 0.875rem 1.75rem; font-size: 1rem; border-radius: var(--radius); }
.btn-block { width: 100%; justify-content: center; }
.btn-gradient {
    background: linear-gradient(135deg, var(--accent), #8b5cf6);
    color: #fff;
    box-shadow: 0 4px 20px var(--accent-glow);
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 0.7rem 1.4rem;
    border-radius: 10px;
    font-weight: 600;
    font-size: 0.95rem;
    cursor: pointer;
    text-decoration: none;
    border: none;
    transition: opacity 0.15s, transform 0.1s;
}
.btn-gradient:hover { opacity: 0.9; transform: translateY(-1px); text-decoration: none; }
.btn-gradient.btn-lg { padding: 0.9rem 1.8rem; font-size: 1rem; }
.btn-gradient.btn-block { width: 100%; display: flex; }

/* ── Forms ── */
.form-group { margin-bottom: 1rem; }
.form-label {
    display: block;
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-secondary);
    margin-bottom: 0.375rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}
.form-input {
    width: 100%;
    padding: 0.75rem 1rem;
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    color: var(--text-primary);
    font-size: 0.9rem;
    outline: none;
    transition: border-color 0.15s;
}
.form-input:focus { border-color: var(--accent); }
.form-input::placeholder { color: var(--text-muted); }
.form-error {
    font-size: 0.8rem;
    color: var(--error);
    margin-top: 0.375rem;
    display: none;
}
.form-error.show { display: block; }

/* ── Auth pages ── */
.auth-page {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 1.5rem;
    position: relative;
    z-index: 1;
}
.auth-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 2rem;
    width: 100%;
    max-width: 420px;
    box-shadow: var(--shadow);
}
.auth-logo {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    margin-bottom: 1.75rem;
    text-decoration: none;
}
.auth-logo-icon {
    width: 36px;
    height: 36px;
    background: linear-gradient(135deg, var(--accent), #8b5cf6);
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
}
.auth-logo-icon svg { width: 20px; height: 20px; color: #fff; }
.auth-logo-text { font-weight: 700; font-size: 1rem; color: var(--text-primary); }
.auth-title { font-size: 1.4rem; font-weight: 700; margin-bottom: 0.25rem; }
.auth-sub { font-size: 0.875rem; color: var(--text-secondary); margin-bottom: 1.5rem; }
.auth-footer { text-align: center; margin-top: 1.25rem; font-size: 0.85rem; color: var(--text-muted); }

/* ── Tooltip ── */
.tip {
    border-bottom: 1px dashed var(--accent);
    cursor: help;
    position: relative;
    display: inline;
}
.tip-popup {
    position: fixed;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 0.625rem 0.875rem;
    font-size: 0.8rem;
    color: var(--text-secondary);
    max-width: 280px;
    box-shadow: var(--shadow);
    z-index: 9999;
    pointer-events: none;
    opacity: 0;
    transition: opacity 0.15s;
    line-height: 1.5;
}
.tip-popup.visible { opacity: 1; }

/* ── Landing page ── */
.landing-nav {
    position: sticky;
    top: 0;
    z-index: 100;
    background: rgba(10,10,15,0.85);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--border);
    padding: 0 2rem;
    height: 60px;
    display: flex;
    align-items: center;
    justify-content: space-between;
}
.landing-logo {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    font-weight: 700;
    font-size: 1rem;
    color: var(--text-primary);
    text-decoration: none;
}
.landing-logo-icon {
    width: 32px;
    height: 32px;
    background: linear-gradient(135deg, var(--accent), #8b5cf6);
    border-radius: 8px;
    display: flex;
    align-items: center;
    justify-content: center;
}
.landing-logo-icon svg { width: 18px; height: 18px; color: #fff; }
.landing-nav-links { display: flex; align-items: center; gap: 1rem; }

.landing-hero {
    text-align: center;
    padding: 6rem 1.5rem 4rem;
    position: relative;
    z-index: 1;
}
.landing-badge {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    background: var(--accent-dim);
    border: 1px solid var(--accent-glow);
    border-radius: 999px;
    padding: 0.3rem 0.875rem;
    font-size: 0.75rem;
    color: var(--accent);
    font-weight: 600;
    margin-bottom: 1.5rem;
}
.landing-h1 {
    font-size: clamp(2rem, 5vw, 3.5rem);
    font-weight: 800;
    line-height: 1.15;
    margin-bottom: 1.25rem;
    background: linear-gradient(135deg, #fff 40%, #a5b4fc);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}
.landing-sub {
    font-size: 1.125rem;
    color: var(--text-secondary);
    max-width: 560px;
    margin: 0 auto 2.5rem;
    line-height: 1.7;
}
.landing-cta { display: flex; gap: 1rem; justify-content: center; flex-wrap: wrap; }

.landing-section {
    max-width: 900px;
    margin: 0 auto;
    padding: 4rem 1.5rem;
    position: relative;
    z-index: 1;
}
.landing-section-label {
    font-size: 0.7rem;
    font-weight: 700;
    letter-spacing: 0.1em;
    text-transform: uppercase;
    color: var(--accent);
    margin-bottom: 0.75rem;
}
.landing-section-title {
    font-size: 1.75rem;
    font-weight: 700;
    margin-bottom: 0.75rem;
}
.landing-section-sub {
    font-size: 1rem;
    color: var(--text-secondary);
    margin-bottom: 2rem;
}

/* ── What's included grid ── */
.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
    gap: 1rem;
}
.feature-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 1.25rem;
    transition: border-color 0.15s;
}
.feature-card:hover { border-color: rgba(99,102,241,0.35); }
.feature-icon {
    width: 36px;
    height: 36px;
    background: var(--accent-dim);
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 0.875rem;
}
.feature-icon svg { width: 18px; height: 18px; color: var(--accent); }
.feature-title { font-weight: 600; font-size: 0.9rem; margin-bottom: 0.3rem; }
.feature-desc { font-size: 0.82rem; color: var(--text-secondary); line-height: 1.5; }

/* ── Pricing card ── */
.pricing-card {
    background: var(--bg-card);
    border: 1px solid var(--accent);
    border-radius: var(--radius);
    padding: 2rem;
    max-width: 380px;
    margin: 0 auto;
    box-shadow: 0 0 40px var(--accent-glow);
    text-align: center;
}
.pricing-badge {
    background: var(--accent);
    color: #fff;
    font-size: 0.7rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    padding: 0.2rem 0.6rem;
    border-radius: 999px;
    display: inline-block;
    margin-bottom: 1rem;
}
.pricing-price {
    font-size: 3rem;
    font-weight: 800;
    color: var(--text-primary);
}
.pricing-price span { font-size: 1rem; font-weight: 400; color: var(--text-muted); }
.pricing-trial { font-size: 0.85rem; color: var(--accent); font-weight: 600; margin: 0.25rem 0 1.25rem; }
.pricing-list { list-style: none; text-align: left; margin-bottom: 1.75rem; }
.pricing-list li {
    display: flex;
    align-items: flex-start;
    gap: 0.625rem;
    font-size: 0.875rem;
    color: var(--text-secondary);
    margin-bottom: 0.625rem;
}
.pricing-list li::before {
    content: '✓';
    color: var(--success);
    font-weight: 700;
    flex-shrink: 0;
    margin-top: 1px;
}

/* ── Course outline preview ── */
.outline-list { list-style: none; }
.outline-chapter {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    margin-bottom: 0.5rem;
    overflow: hidden;
}
.outline-chapter-header {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    padding: 0.875rem 1rem;
    font-size: 0.875rem;
    font-weight: 600;
}
.outline-free-badge {
    margin-left: auto;
    font-size: 0.65rem;
    font-weight: 700;
    background: rgba(34,197,94,0.12);
    color: var(--success);
    border: 1px solid rgba(34,197,94,0.25);
    border-radius: 999px;
    padding: 0.15rem 0.5rem;
    text-transform: uppercase;
    letter-spacing: 0.06em;
}
.outline-lock {
    margin-left: auto;
    color: var(--text-muted);
    font-size: 0.8rem;
}

footer.landing-footer {
    border-top: 1px solid var(--border);
    text-align: center;
    padding: 2rem;
    font-size: 0.8rem;
    color: var(--text-muted);
    position: relative;
    z-index: 1;
}

@media (max-width: 600px) {
    .landing-hero { padding: 4rem 1rem 2.5rem; }
    .features-grid { grid-template-columns: 1fr 1fr; }
}