/* ═══════════════════════════════════════════════════════════
   UNIVERSAL COURSE LIGHT THEME — matches homepage aesthetic.
   Each course sets --course-primary and --course-accent via
   a tiny inline <style> or their own styles.css override.
   ═══════════════════════════════════════════════════════════ */
@import url('https://fonts.googleapis.com/css2?family=Nunito:wght@400;500;600;700;800&family=Fira+Code:wght@400;500&display=swap');

:root {
    --course-primary: #6366f1;
    --course-accent:  #818cf8;
    --bg-page: linear-gradient(160deg, #f8fafc 0%, #eef2ff 40%, #f5f3ff 70%, #fce7f3 100%);
    --bg-card: rgba(255,255,255,0.7);
    --bg-card-hover: rgba(255,255,255,0.9);
    --border-subtle: rgba(0,0,0,0.06);
    --text-primary: #1e293b;
    --text-secondary: #475569;
    --text-muted: #64748b;
    --text-light: #94a3b8;
    --code-bg: #1e293b;
    --shadow-card: 0 2px 12px rgba(0,0,0,0.04), 0 1px 3px rgba(0,0,0,0.03);
}

* { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }

body {
    font-family: 'Nunito', sans-serif;
    background: var(--bg-page);
    min-height: 100vh;
    padding: 20px;
    color: var(--text-primary);
    line-height: 1.8;
}

.page-bg-particles { position: fixed; inset: 0; z-index: 0; pointer-events: none; overflow: hidden; }
.page-bg-particles .orb {
    position: absolute; border-radius: 50%; filter: blur(100px); opacity: 0.08;
    animation: orbFloat 20s ease-in-out infinite alternate;
}
.page-bg-particles .orb:nth-child(1) { width: 500px; height: 500px; background: var(--course-primary); top: -10%; left: -10%; }
.page-bg-particles .orb:nth-child(2) { width: 400px; height: 400px; background: var(--course-accent); bottom: -15%; right: -10%; animation-delay: -7s; }
.page-bg-particles .orb:nth-child(3) { width: 300px; height: 300px; background: var(--course-primary); top: 50%; left: 50%; animation-delay: -14s; }
@keyframes orbFloat { 0% { transform: translate(0,0) scale(1); } 50% { transform: translate(30px,-30px) scale(1.1); } 100% { transform: translate(-20px,20px) scale(0.95); } }

.container { max-width: 1000px; margin: 0 auto; position: relative; z-index: 1; }

/* ── Navigation ── */
.nav {
    background: rgba(255,255,255,0.8);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    padding: 15px 30px;
    border-radius: 15px;
    margin-bottom: 30px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border: 1px solid rgba(0,0,0,0.06);
    box-shadow: var(--shadow-card);
}
.nav a { color: var(--course-primary); text-decoration: none; font-weight: 600; display: flex; align-items: center; gap: 8px; transition: all 0.3s; }
.nav a:hover { color: var(--course-accent); }

/* ── Hero ── */
.lesson-hero {
    text-align: center; padding: 50px 40px;
    background: rgba(255,255,255,0.6);
    backdrop-filter: blur(10px);
    border-radius: 25px; margin-bottom: 40px;
    border: 1px solid rgba(0,0,0,0.05);
    position: relative; overflow: hidden;
    box-shadow: 0 4px 24px rgba(0,0,0,0.04);
}
.lesson-hero h1 {
    font-size: 2.8em; margin-bottom: 15px; font-weight: 900;
    background: linear-gradient(135deg, var(--course-primary), var(--course-accent));
    -webkit-background-clip: text; -webkit-text-fill-color: transparent;
    background-clip: text;
}
.lesson-hero p { font-size: 1.3em; color: var(--text-secondary); max-width: 700px; margin: 0 auto; }

/* ── Sections ── */
.section {
    background: var(--bg-card);
    border-radius: 20px; padding: 40px; margin-bottom: 30px;
    border: 1px solid var(--border-subtle);
    box-shadow: var(--shadow-card);
    opacity: 1;
}
.section.visible { opacity: 1; }
.section h2 { color: var(--course-primary); font-size: 2em; margin-bottom: 20px; display: flex; align-items: center; gap: 12px; }
.section h3 { color: var(--course-accent); font-size: 1.4em; margin: 25px 0 15px; }

/* ── ELI5 Box ── */
.eli5-box {
    background: linear-gradient(135deg, rgba(99,102,241,0.04), rgba(139,92,246,0.03));
    border-radius: 20px; padding: 30px; margin: 25px 0;
    border: 2px dashed rgba(99,102,241,0.15);
}
.eli5-box h4 { color: var(--course-primary); margin-bottom: 12px; font-size: 1.2em; }
.eli5-box p { color: var(--text-secondary); line-height: 1.8; }

/* ── Real Life ── */
.real-life {
    background: linear-gradient(135deg, rgba(59,130,246,0.06), rgba(96,165,250,0.04));
    border-radius: 16px; padding: 25px; margin: 20px 0;
    border-left: 4px solid #3b82f6;
}
.real-life h4 { color: #2563eb; margin-bottom: 10px; }
.real-life p { color: var(--text-secondary); }

/* ── Important Box ── */
.important-box {
    background: linear-gradient(135deg, rgba(239,68,68,0.05), rgba(248,113,113,0.03));
    border-radius: 16px; padding: 25px; margin: 20px 0;
    border-left: 4px solid #ef4444;
}
.important-box h4 { color: #dc2626; margin-bottom: 10px; }
.important-box p { color: var(--text-secondary); }

/* ── Pro Tip ── */
.pro-tip {
    background: linear-gradient(135deg, rgba(34,197,94,0.05), rgba(74,222,128,0.03));
    border-radius: 16px; padding: 25px; margin: 20px 0;
    border-left: 4px solid #22c55e;
}
.pro-tip h4 { color: #16a34a; margin-bottom: 10px; }
.pro-tip p { color: var(--text-secondary); }

/* ── Code Block ── */
.code-block {
    background: var(--code-bg); border-radius: 12px; padding: 20px; margin: 15px 0;
    overflow-x: auto; font-family: 'Fira Code', monospace; font-size: 0.9em;
    border: 1px solid #334155; box-shadow: 0 4px 16px rgba(0,0,0,0.08);
}
.code-block pre { margin: 0; color: #f8fafc; white-space: pre; }

/* Syntax highlight colors (keep bright on dark code bg) */
.code-block .keyword { color: #c084fc; font-weight: 600; }
.code-block .string { color: #86efac; }
.code-block .comment { color: #64748b; font-style: italic; }
.code-block .function { color: #67e8f9; }
.code-block .number { color: #fbbf24; }
.code-block .type { color: #7dd3fc; }
.code-block .operator { color: #fca5a5; }

/* ── Tables ── */
.comparison-table { width: 100%; border-collapse: collapse; margin: 20px 0; border-radius: 12px; overflow: hidden; }
.comparison-table th { background: rgba(99,102,241,0.08); color: var(--course-primary); padding: 14px 18px; text-align: left; font-weight: 700; }
.comparison-table td { padding: 12px 18px; border-bottom: 1px solid var(--border-subtle); color: var(--text-secondary); }
.comparison-table tr:hover td { background: rgba(99,102,241,0.03); }

.result-table { width: 100%; border-collapse: collapse; margin: 15px 0; border-radius: 12px; overflow: hidden; }
.result-table th { background: rgba(99,102,241,0.08); color: var(--course-primary); padding: 10px 16px; text-align: left; font-weight: 700; font-size: 0.9em; }
.result-table td { padding: 10px 16px; border-bottom: 1px solid var(--border-subtle); color: var(--text-secondary); font-size: 0.9em; }
.result-table tr:hover td { background: rgba(99,102,241,0.03); }

/* ── Stats Grid ── */
.stats-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 15px; margin: 20px 0; }
.stat-card {
    background: rgba(255,255,255,0.8); border: 1px solid var(--border-subtle);
    border-radius: 12px; padding: 20px; text-align: center;
    box-shadow: var(--shadow-card);
}
.stat-card .stat-number { font-size: 2em; font-weight: 900; color: var(--course-primary); }
.stat-card .stat-label { color: var(--text-muted); font-size: 0.9em; margin-top: 5px; }

/* ── Step Box ── */
.step-box {
    background: rgba(255,255,255,0.6); border-radius: 16px;
    padding: 25px 25px 25px 70px; margin: 20px 0;
    border: 1px solid var(--border-subtle);
    counter-increment: step-counter; position: relative;
    box-shadow: var(--shadow-card);
}
.step-box::before {
    content: counter(step-counter); position: absolute; left: 20px; top: 20px;
    width: 36px; height: 36px;
    background: linear-gradient(135deg, var(--course-primary), var(--course-accent));
    color: #fff; border-radius: 50%;
    display: flex; align-items: center; justify-content: center; font-weight: 800;
}

/* ── Quiz ── */
.quiz-section {
    background: rgba(255,255,255,0.6); border-radius: 20px;
    padding: 30px; margin: 30px 0;
    border: 1px solid var(--border-subtle);
    box-shadow: var(--shadow-card);
}
.quiz-option {
    display: block; padding: 12px 20px; margin: 8px 0;
    background: rgba(255,255,255,0.8);
    border: 2px solid rgba(0,0,0,0.08);
    border-radius: 12px; color: var(--text-primary);
    cursor: pointer; transition: all 0.3s;
    font-size: 1em; text-align: left; width: 100%; font-family: inherit;
}
.quiz-option:hover { border-color: var(--course-primary); background: rgba(99,102,241,0.04); }
.quiz-option.correct { border-color: #22c55e; background: rgba(34,197,94,0.08); }
.quiz-option.wrong { border-color: #ef4444; background: rgba(239,68,68,0.05); }
.quiz-option:disabled { cursor: default; opacity: 0.7; }

/* Alternate quiz styles (for inline quiz boxes) */
.quiz-box { background: rgba(255,255,255,0.6); border-radius: 16px; padding: 24px; margin: 20px 0; border: 1px solid var(--border-subtle); box-shadow: var(--shadow-card); }
.quiz-q { color: var(--course-primary); margin-bottom: 14px; font-size: 1.15em; font-weight: 700; }
.quiz-opt { display: block; width: 100%; text-align: left; padding: 12px 18px; margin: 8px 0; background: rgba(255,255,255,0.8); border: 2px solid rgba(0,0,0,0.08); border-radius: 10px; color: var(--text-primary); cursor: pointer; font-family: inherit; font-size: 0.95em; transition: all 0.2s; }
.quiz-opt:hover { border-color: var(--course-primary); background: rgba(99,102,241,0.04); }
.quiz-opt.correct { border-color: #22c55e; background: rgba(34,197,94,0.08); }
.quiz-opt.wrong { border-color: #ef4444; background: rgba(239,68,68,0.05); }
.quiz-opt:disabled { cursor: default; opacity: 0.7; }
.quiz-fb { display: none; margin-top: 10px; padding: 12px; border-radius: 8px; font-weight: 600; }

/* ── Lesson Navigation ── */
.lesson-nav {
    display: flex; justify-content: space-between; align-items: center;
    margin-top: 40px; padding-top: 30px;
    border-top: 1px solid var(--border-subtle);
}
.lesson-nav a {
    display: inline-flex; align-items: center; gap: 8px;
    padding: 14px 28px;
    background: linear-gradient(135deg, var(--course-primary), var(--course-accent));
    color: #fff; border-radius: 12px; text-decoration: none;
    font-weight: 700; transition: all 0.3s;
    box-shadow: 0 4px 14px rgba(99,102,241,0.2);
}
.lesson-nav a:hover { transform: translateY(-2px); box-shadow: 0 8px 24px rgba(99,102,241,0.3); }
.lesson-nav a.secondary { background: rgba(255,255,255,0.8); color: var(--text-primary); border: 1px solid var(--border-subtle); box-shadow: var(--shadow-card); }
.lesson-nav a.secondary:hover { background: #fff; }

/* ── Pro CTA Banner (shown in paywall-gated pages) ── */
.pro-cta-banner {
    background: linear-gradient(135deg, rgba(99,102,241,0.08), rgba(139,92,246,0.06));
    border: 1px solid rgba(99,102,241,0.15);
    border-radius: 16px; padding: 20px 28px; margin: 30px 0;
    text-align: center;
}
.pro-cta-banner p { color: var(--text-secondary); margin: 0 0 10px; }
.pro-cta-banner a {
    display: inline-block; padding: 10px 24px;
    background: linear-gradient(135deg, #6366f1, #8b5cf6);
    color: #fff; border-radius: 10px;
    font-weight: 700; text-decoration: none; font-size: 0.9rem;
    box-shadow: 0 4px 14px rgba(99,102,241,0.3);
}

/* ── Responsive ── */
.nav a:focus-visible,
.lesson-nav a:focus-visible,
.quiz-option:focus-visible,
.quiz-opt:focus-visible {
    outline: 2px solid var(--course-primary, #4f46e5);
    outline-offset: 3px;
}

.comparison-table,
.result-table,
.code-block {
    max-width: 100%;
}

@media (max-width: 768px) {
    .lesson-hero { padding: 32px 18px; }
    .lesson-hero h1 { font-size: 2em; }
    .section { padding: 25px 18px; }
    .lesson-nav { flex-direction: column; gap: 12px; align-items: stretch; }
    .lesson-nav a { width: 100%; justify-content: center; }
    .nav { padding: 12px 14px; gap: 10px; flex-wrap: wrap; }
    body { padding: 12px; }
}

/* Additive lesson foundation. Existing .quiz-opt / .quiz-option rules stay. */

body.dfd-safe {
    padding-left: max(20px, env(safe-area-inset-left, 0px));
    padding-right: max(20px, env(safe-area-inset-right, 0px));
    padding-bottom: max(20px, env(safe-area-inset-bottom, 0px));
}

.dfd-hit,
.dfd-quiz-choice,
.dfd-back-top,
.dfd-diagram-control,
[data-dfd-complete] {
    min-width: 48px;
    min-height: 48px;
    touch-action: manipulation;
}

.dfd-quiz {
    background: rgba(255,255,255,0.7);
    border: 1px solid var(--border-subtle);
    border-radius: 16px;
    padding: 24px;
    margin: 24px 0;
    box-shadow: var(--shadow-card);
    max-width: 100%;
}

.dfd-quiz-choice {
    display: block;
    width: 100%;
    margin: 8px 0;
    padding: 12px 16px;
    text-align: left;
    font-family: inherit;
    font-size: 1rem;
    font-weight: 700;
    color: var(--text-primary);
    background: rgba(255,255,255,0.9);
    border: 2px solid rgba(0,0,0,0.08);
    border-radius: 12px;
    overflow-wrap: anywhere;
    cursor: pointer;
}

.dfd-quiz-choice:hover { border-color: var(--course-primary); }
.dfd-quiz-choice.dfd-quiz-correct { border-color: #15803d; background: #f0fdf4; }
.dfd-quiz-choice.dfd-quiz-wrong { border-color: #b91c1c; background: #fef2f2; }
.dfd-quiz-feedback, .dfd-quiz-explain { margin-top: 12px; font-weight: 700; overflow-wrap: anywhere; }

.dfd-lesson-progress { margin: 20px 0; }
.dfd-lesson-progress-track {
    height: 12px;
    border-radius: 999px;
    background: rgba(15, 23, 42, 0.08);
    overflow: hidden;
}
.dfd-lesson-progress-fill {
    height: 100%;
    width: 0;
    background: linear-gradient(90deg, var(--course-primary), var(--course-accent));
}

.dfd-diagram { max-width: 100%; overflow-x: auto; -webkit-overflow-scrolling: touch; }
.dfd-diagram svg, svg.dfd-responsive { display: block; max-width: 100%; height: auto; }
.dfd-diagram-controls { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 12px; }
.dfd-diagram-control {
    padding: 10px 16px;
    border-radius: 12px;
    border: 2px solid rgba(0,0,0,0.08);
    background: #fff;
    font-family: inherit;
    font-weight: 700;
    color: var(--text-primary);
    cursor: pointer;
}
.dfd-diagram-control.dfd-diagram-active { border-color: var(--course-primary); color: var(--course-primary); }
.dfd-scroll { display: block; max-width: 100%; overflow-x: auto; -webkit-overflow-scrolling: touch; }
.dfd-back-top {
    position: fixed;
    right: max(16px, env(safe-area-inset-right, 0px));
    bottom: max(16px, env(safe-area-inset-bottom, 0px));
    z-index: 30;
    border: 0;
    border-radius: 999px;
    padding: 0 16px;
    background: var(--course-primary);
    color: #fff;
    font-weight: 800;
    cursor: pointer;
}

@media (prefers-reduced-motion: no-preference) {
    [data-dfd-reveal].dfd-reveal-pending { opacity: 0; transform: translateY(12px); }
    [data-dfd-reveal].dfd-revealed {
        opacity: 1;
        transform: none;
        transition: opacity 420ms ease, transform 420ms ease;
    }
}