:root {
    /* Web 1.0 Retro Palette */
    --bg-color: #fffff4;
    --bg-pattern: rgba(0, 0, 0, 0.08);
    --window-bg: #ffffff;
    --border-color: #000000;
    --shadow-color: #000000;
    --text-color: #000000;
    --text-muted: #555555;
    --accent-primary: #93c5fd;
    --accent-secondary: #fef08a;
    --success-green: #059669;
    --icon-bg: #ffffff;
    --btn-bg: #fef08a;

    /* Exercise Specifics */
    --result-output-bg: #ffffff;
    --pass-bg: #dcfce7;
    --pass-text: #15803d;
    --fail-bg: #fee2e2;
    --fail-text: #991b1b;
}

[data-theme="dark"] {
    --bg-color: #1e1b4b;
    --bg-pattern: rgba(255, 255, 255, 0.1);
    --window-bg: #312e81;
    --border-color: #ffffff;
    --shadow-color: #a5b4fc;
    --text-color: #ffffff;
    --text-muted: #c7d2fe;
    --accent-primary: #818cf8;
    --accent-secondary: #4ade80;
    --icon-bg: #312e81;
    --btn-bg: #4ade80;

    /* Exercise Specifics */
    --result-output-bg: #1e1b4b;
    --pass-bg: #064e3b;
    --pass-text: #4ade80;
    --fail-bg: #7f1d1d;
    --fail-text: #fca5a5;
}

/* ============================================
   GLOBAL RESET
   ============================================ */
*,
*::before,
*::after {
    box-sizing: border-box;
    margin: 0;
}

html {
    overflow-x: hidden;
    /* Absolute safety net */
}

img,
pre,
iframe,
table {
    max-width: 100%;
}

/* ============================================
   BODY — The padding here is the "shadow buffer".
   As long as padding >= max shadow size (8px),
   shadows will never overflow the viewport.
   ============================================ */
body {
    font-family: 'Tahoma', 'Verdana', 'MS Gothic', sans-serif;
    background-color: var(--bg-color);
    background-image:
        linear-gradient(var(--bg-pattern) 1px, transparent 1px),
        linear-gradient(90deg, var(--bg-pattern) 1px, transparent 1px);
    background-size: 24px 24px;
    color: var(--text-color);
    padding: 1rem;
    /* 16px on all sides — always > 8px shadow */
    min-height: 100vh;
    line-height: 1.6;
    overflow-wrap: break-word;
    word-break: break-word;
}

/* ============================================
   LAYOUT — Simple centered column via margin auto.
   No flex centering quirks.
   ============================================ */
header,
footer {
    text-align: center;
    max-width: 800px;
    margin: 0 auto 1rem auto;
}

main {
    max-width: 800px;
    width: 100%;
    margin: 0 auto;
}

footer {
    margin-top: 3rem;
    color: var(--text-muted);
    font-size: 0.9rem;
}

/* ============================================
   THEME TOGGLE
   ============================================ */
.theme-toggle {
    position: fixed;
    top: 0.75rem;
    right: 0.75rem;
    width: 44px;
    height: 44px;
    background: var(--window-bg);
    border: 2px solid var(--border-color);
    color: var(--text-color);
    font-size: 1.2rem;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    z-index: 1000;
    box-shadow: 3px 3px 0px var(--shadow-color);
}

/* ============================================
   MAIN TITLE
   ============================================ */
h1.main-title {
    font-size: clamp(1.2rem, 5vw, 2.2rem);
    display: inline-block;
    background: var(--window-bg);
    border: 3px solid var(--border-color);
    padding: 10px 20px;
    box-shadow: 6px 6px 0px var(--shadow-color);
    margin-bottom: 1.5rem;
}

/* ============================================
   RETRO WINDOW — The core container.
   width: 100% means it fills <main>, which is
   already max-width 800px and within body padding.
   ============================================ */
.retro-window {
    background: var(--window-bg);
    border: 3px solid var(--border-color);
    box-shadow: clamp(4px, 1vw, 8px) clamp(4px, 1vw, 8px) 0px var(--shadow-color);
    width: 100%;
    margin-bottom: 2rem;
    padding: 1.5rem;
}

/* ============================================
   LESSON CONTENT
   ============================================ */
.lesson-body {
    line-height: 1.8;
    font-size: clamp(1rem, 2.5vw, 1.1rem);
}

.lesson-body h1 {
    font-size: clamp(1.3rem, 4vw, 1.8rem);
    margin: 0.5rem 0 1rem 0;
}

.lesson-body h2 {
    background: var(--accent-primary);
    display: inline-block;
    padding: 4px 12px;
    border: 2px solid var(--border-color);
    margin-top: 2rem;
    margin-bottom: 0.5rem;
    font-size: clamp(1.1rem, 3vw, 1.4rem);
    max-width: 100%;
}

[data-theme="dark"] .lesson-body h2 {
    color: #000;
}

.lesson-body h3 {
    font-size: clamp(1rem, 2.5vw, 1.2rem);
    margin-top: 1.5rem;
}

.lesson-body code {
    background: var(--accent-secondary);
    color: #000;
    padding: 2px 5px;
    border: 1px solid var(--border-color);
    font-family: 'Courier New', Courier, monospace;
    font-size: 0.9em;
}

.lesson-body pre {
    background: #1e1e1e;
    color: #d4d4d4;
    padding: 1rem;
    border: 2px solid var(--border-color);
    box-shadow: 4px 4px 0px var(--shadow-color);
    overflow-x: auto;
    font-size: 0.85em;
}

.lesson-body pre code {
    background: none;
    border: none;
    color: inherit;
    padding: 0;
}

.lesson-body blockquote {
    border-left: 4px solid var(--accent-primary);
    padding: 0.5rem 1rem;
    margin: 1rem 0;
    background: var(--window-bg);
}

.lesson-body hr {
    border: none;
    border-top: 2px dashed var(--border-color);
    margin: 2rem 0;
}

.lesson-body p {
    margin: 0.75rem 0;
}

.lesson-body ul,
.lesson-body ol {
    padding-left: 1.5rem;
}

.lesson-body li {
    margin: 0.3rem 0;
}

/* ============================================
   PROGRESS BUTTON
   ============================================ */
.btn-complete {
    background: var(--accent-secondary);
    border: 3px solid var(--border-color);
    padding: 12px 24px;
    font-weight: bold;
    cursor: pointer;
    box-shadow: 4px 4px 0px var(--shadow-color);
    margin-top: 2rem;
    width: 100%;
    font-size: 1.1rem;
    color: var(--text-color);
}

.btn-complete.active {
    background: var(--success-green);
    color: white;
}

/* ============================================
   INDEX — Lesson List
   ============================================ */
.lesson-item {
    display: flex;
    gap: 0.75rem;
    padding: 0.75rem;
    border-bottom: 2px dashed var(--border-color);
    text-decoration: none;
    color: var(--text-color);
    align-items: center;
}

.lesson-item:hover {
    background: var(--accent-primary);
    color: #000;
}

.lesson-item .lesson-info h3 {
    margin: 0;
    font-size: 1.1rem;
}

.lesson-item .lesson-info p {
    margin: 4px 0 0 0;
    font-size: 0.85rem;
    color: var(--text-muted);
}

/* ============================================
   EXERCISE EMBEDDING
   ============================================ */
.exercise-embed {
    margin: 2rem 0;
    width: 100%;
    border: 3px solid var(--border-color);
    box-shadow: 6px 6px 0px var(--shadow-color);
    overflow: hidden;
}

.exercise-iframe {
    width: 100%;
    height: 600px;
    border: none;
    display: block;
    background: white;
}



.exercise-mobile-choice {
    display: none;
    gap: 10px;
    margin: 1.5rem 0;
}

.ex-mobile-btn-main,
.ex-mobile-btn-ext {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 12px 10px;
    text-decoration: none;
    font-weight: bold;
    border: 3px solid var(--border-color);
    box-shadow: 4px 4px 0px var(--shadow-color);
    font-size: 14px;
}

.ex-mobile-btn-main {
    background: var(--btn-bg);
    color: #000;
}

.ex-mobile-btn-ext {
    background: var(--accent-secondary);
    color: #000;
}

.ex-mobile-btn-main:hover,
.ex-mobile-btn-ext:hover {
    filter: brightness(1.1);
}

@media (max-width: 830px) {
    .exercise-embed {
        display: none;
    }

    .exercise-mobile-link {
        display: block;
    }

    .exercise-mobile-choice {
        display: flex;
    }
}

/* Fullscreen overlay */
.exercise-embed.fullscreen {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 10000;
    margin: 0;
    border: none;
    box-shadow: none;
}

.exercise-embed.fullscreen .exercise-iframe {
    height: 100vh;
}

/* ============================================
   LESSON NAVIGATION
   ============================================ */
.lesson-navigation {
    display: flex;
    gap: 0.5rem;
    max-width: 800px;
    width: 100%;
    margin: 0 auto 2rem auto;
}

.lesson-navigation>* {
    flex: 1;
    min-width: 0;
}

.nav-btn {
    display: block;
    padding: 10px;
    text-decoration: none;
    text-align: center;
    color: var(--text-color);
    background: var(--window-bg);
    border: 3px solid var(--border-color);
    box-shadow: 4px 4px 0px var(--shadow-color);
}

.nav-btn:hover {
    background: var(--accent-primary);
    color: #000;
}

.nav-placeholder {
    flex: 1;
}

/* ============================================
   LESSON PAGE — Back Link & Exercise List
   ============================================ */
.back-link-container {
    margin-bottom: 1.5rem;
}

.back-link {
    color: var(--text-muted);
    font-weight: bold;
    text-decoration: none;
}

.back-link:hover {
    color: var(--text-color);
}

.exercise-list-section {
    margin-top: 3rem;
    border-top: 3px dashed var(--border-color);
    padding-top: 2rem;
}

.exercise-list-title {
    background: var(--accent-secondary) !important;
    color: #000 !important;
}

.exercise-list-item {
    display: flex;
    margin-top: 10px;
    border: 3px solid var(--border-color);
    box-shadow: 4px 4px 0px var(--shadow-color);
    background: var(--window-bg);
}

.ex-item-main {
    flex: 1;
    display: flex;
    align-items: center;
    padding: 12px;
    text-decoration: none;
    color: var(--text-color);
    font-weight: bold;
}

.ex-item-main:hover {
    background: var(--accent-primary);
    color: #000;
}

.ex-item-external {
    display: flex;
    align-items: center;
    justify-content: center;
    width: auto;
    padding: 0 15px;
    border-left: 3px solid var(--border-color);
    text-decoration: none;
    color: var(--text-color);
    font-size: 14px;
    font-weight: bold;
    background: var(--accent-secondary);
}

.ex-item-external:hover {
    filter: brightness(1.1);
    background: var(--accent-primary);
}

/* ============================================
   BREADCRUMBS
   ============================================ */
.breadcrumb {
    display: flex;
    align-items: center;
    gap: 8px;
    margin-bottom: 1.5rem;
    font-size: 0.9rem;
    color: var(--text-muted);
    flex-wrap: wrap;
    background: var(--window-bg);
    padding: 8px 12px;
    border: 2px solid var(--border-color);
    box-shadow: 3px 3px 0px var(--shadow-color);
}

.breadcrumb a {
    color: var(--text-color);
    text-decoration: none;
    font-weight: bold;
    display: flex;
    align-items: center;
    gap: 5px;
}

.breadcrumb a:hover {
    text-decoration: underline;
    color: var(--accent-primary);
}

.breadcrumb-sep {
    color: var(--text-muted);
    font-weight: normal;
}

.breadcrumb-logo {
    width: 20px;
    height: 20px;
    object-fit: contain;
}

.breadcrumb-current {
    color: var(--text-muted);
    font-weight: normal;
}

@media (max-width: 600px) {
    .breadcrumb-text-home {
        display: none;
        /* Hide long text on mobile, keep logo */
    }

    .breadcrumb {
        padding: 6px 10px;
        font-size: 0.85rem;
        gap: 5px;
    }
}