/* ==========================================
   Shared Styles
   ========================================== */

/* --- Design Tokens (3.2) --- */
:root {
    --color-primary: #1a1a2e;
    --color-primary-light: #16213e;
    --color-primary-border: #0f3460;
    --color-accent: #e94560;
    --color-success: #4caf50;
    --color-success-hover: #43a047;
    --color-danger: #f44336;
    --color-danger-hover: #d32f2f;
    --color-warning: #ff9800;
    --color-warning-hover: #f57c00;
    --color-info: #2196f3;
    --color-info-hover: #1976d2;
    --color-bg: #f4f4f4;
    --color-surface: #fff;
    --color-surface-alt: #f5f5f5;
    --color-surface-dark: #0f0f1e;
    --color-border: #e0e0e0;
    --color-border-light: #eee;
    --color-text: #333;
    --color-text-muted: #555;
    --color-text-light: #666;
    --color-text-lighter: #777;
    --font-mono: 'Courier New', Courier, monospace;
    --font-sans: 'Segoe UI', Arial, sans-serif;
    --radius-sm: 4px;
    --radius-md: 6px;
    --radius-lg: 8px;
}

* {
    box-sizing: border-box;
}

body {
    font-family: var(--font-sans);
    line-height: 1.6;
    margin: 0;
    padding: 0;
    background-color: var(--color-bg);
    color: var(--color-text);
}

/* --- Accessibility: Focus Rings (2.2) --- */
button:focus-visible,
[role="switch"]:focus-visible,
[role="radiogroup"] button:focus-visible,
a:focus-visible,
input[type="range"]:focus-visible {
    outline: 2px solid var(--color-accent);
    outline-offset: 2px;
}

/* --- Utility: Hidden (2.6) --- */
.hidden {
    display: none !important;
}

/* --- Utility: Screen Reader Only (2.5) --- */
.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

/* --- Header --- */
header {
    background-color: var(--color-primary);
    color: #fff;
    padding: 1rem 0;
    text-align: center;
}

header h1 {
    margin: 0;
    font-size: 1.8rem;
}

header p {
    margin: 0.3rem 0 0;
    opacity: 0.8;
    font-size: 0.95rem;
}

/* --- Navigation --- */
nav {
    background-color: var(--color-primary-light);
    padding: 0;
    display: flex;
    justify-content: center;
    gap: 0;
    border-bottom: 2px solid var(--color-primary-border);
}

nav a {
    color: #ccc;
    text-decoration: none;
    padding: 0.75rem 1.5rem;
    font-size: 0.95rem;
    transition: background-color 0.2s, color 0.2s;
    border-bottom: 2px solid transparent;
    margin-bottom: -2px;
}

nav a:hover {
    background-color: var(--color-primary-border);
    color: #fff;
}

nav a.active {
    color: #fff;
    border-bottom-color: var(--color-accent);
    font-weight: 600;
    background-color: var(--color-primary-border);
}

/* --- Main Content --- */
main {
    padding: 20px;
    max-width: 960px;
    margin: 20px auto;
    background-color: var(--color-surface);
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
    border-radius: var(--radius-sm);
}

section {
    margin-bottom: 20px;
    padding-bottom: 20px;
    border-bottom: 1px solid var(--color-border-light);
}

section:last-child {
    border-bottom: none;
    margin-bottom: 0;
    padding-bottom: 0;
}

h2 {
    color: var(--color-primary);
    margin-top: 0;
}

h3 {
    color: #444;
}

ul, ol {
    margin-left: 20px;
}

/* --- Section Anchor Links (1.2) --- */
.section-nav {
    display: flex;
    gap: 16px;
    padding: 8px 0;
    margin-bottom: 12px;
    border-bottom: 1px solid var(--color-border-light);
    font-size: 0.9rem;
}

.section-nav a {
    color: var(--color-info);
    text-decoration: none;
    font-weight: 600;
}

.section-nav a:hover {
    text-decoration: underline;
}

/* --- Explanation Boxes --- */
.explanation-box {
    background-color: #e7f3fe;
    border-left: 6px solid var(--color-info);
    margin: 20px 0;
    padding: 10px 20px;
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}

.explanation-box h4 {
    margin-top: 0;
    color: var(--color-info);
}

.explanation-box.simple-terms {
    background-color: #fff8e1;
    border-left-color: var(--color-warning);
}

.explanation-box.simple-terms h4 {
    color: #e65100;
}

/* --- Footer (1.3) --- */
footer {
    text-align: center;
    padding: 20px 16px;
    background-color: var(--color-primary);
    color: #fff;
    margin-top: 20px;
    font-size: 0.9rem;
}

footer > p {
    margin: 0 0 12px;
}

footer a {
    color: var(--color-accent);
    text-decoration: none;
}

footer a:hover {
    text-decoration: underline;
}

.footer-nav {
    display: flex;
    justify-content: center;
    gap: 0;
}

.footer-nav a {
    color: #ccc;
    padding: 10px 20px;
    font-size: 0.9rem;
    border-radius: var(--radius-sm);
    transition: background-color 0.15s, color 0.15s;
}

.footer-nav a:hover {
    color: #fff;
    background-color: rgba(255, 255, 255, 0.1);
    text-decoration: none;
}

/* --- Shared Simulator Config (3.1) --- */
.sim-config {
    display: flex;
    flex-wrap: wrap;
    gap: 16px;
    align-items: center;
    margin-bottom: 12px;
    padding: 12px 16px;
    background: var(--color-surface-alt);
    border-radius: var(--radius-md);
    border: 1px solid var(--color-border);
}

.config-group {
    display: flex;
    align-items: center;
    gap: 10px;
}

.config-group > label {
    font-weight: 600;
    font-size: 0.9rem;
    color: var(--color-text-muted);
    white-space: nowrap;
}

/* --- Shared Segmented Button Group (3.1) --- */
[role="radiogroup"] {
    display: flex;
    gap: 4px;
    background: #e8e8ee;
    border-radius: var(--radius-lg);
    padding: 3px;
}

.seg-btn {
    padding: 8px 16px;
    border: 2px solid transparent;
    background: transparent;
    cursor: pointer;
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--color-text-light);
    transition: background 0.15s, color 0.15s, border-color 0.15s, box-shadow 0.15s, opacity 0.15s;
    border-radius: var(--radius-md);
    -webkit-tap-highlight-color: transparent;
}

.seg-btn:active {
    opacity: 0.7;
}

.seg-btn.active {
    background: var(--color-accent);
    color: #fff;
    border-color: var(--color-accent);
    box-shadow: 0 2px 8px rgba(233, 69, 96, 0.35);
}

.seg-btn:not(.active):active {
    background: rgba(0, 0, 0, 0.08);
}

/* --- Shared Control Buttons (3.1) --- */
.control-buttons {
    display: flex;
    gap: 8px;
}

.ctrl-btn {
    padding: 8px 18px;
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 0.9rem;
    font-weight: 600;
    color: #fff;
    transition: background-color 0.15s;
}

.ctrl-btn.play { background: var(--color-success); }
.ctrl-btn.play:hover { background: var(--color-success-hover); }
.ctrl-btn.pause { background: var(--color-warning); }
.ctrl-btn.pause:hover { background: var(--color-warning-hover); }
.ctrl-btn.step { background: var(--color-info); }
.ctrl-btn.step:hover { background: var(--color-info-hover); }
.ctrl-btn.reset { background: var(--color-danger); }
.ctrl-btn.reset:hover { background: var(--color-danger-hover); }

.ctrl-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* --- Shared Speed Control (3.1) --- */
.speed-control {
    display: flex;
    align-items: center;
    gap: 8px;
    margin-left: auto;
}

.speed-control label {
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--color-text-muted);
}

.speed-control input[type="range"] {
    width: 100px;
    accent-color: var(--color-primary);
}

.speed-label {
    font-size: 0.8rem;
    color: var(--color-text-lighter);
    min-width: 45px;
}

/* --- Keyboard Shortcuts Hint (5.3) --- */
.keyboard-hint {
    font-size: 0.8rem;
    color: var(--color-text-lighter);
    margin-top: 4px;
}

.keyboard-hint kbd {
    display: inline-block;
    padding: 1px 6px;
    border: 1px solid #ccc;
    border-radius: 3px;
    background: var(--color-surface-alt);
    font-family: var(--font-mono);
    font-size: 0.75rem;
}

/* --- Further Reading (6.2) --- */
.further-reading {
    margin-top: 20px;
    padding: 16px 20px;
    background: var(--color-surface-alt);
    border-radius: var(--radius-md);
    border: 1px solid var(--color-border);
}

.further-reading h3 {
    margin-top: 0;
    font-size: 1rem;
}

.further-reading ul {
    margin: 8px 0 0;
    padding-left: 20px;
}

.further-reading li {
    margin-bottom: 4px;
    font-size: 0.9rem;
}

.further-reading a {
    color: var(--color-info);
    text-decoration: none;
}

.further-reading a:hover {
    text-decoration: underline;
}

/* --- Landing page card grid --- */
.card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(min(280px, 100%), 1fr));
    gap: 24px;
    padding: 10px 0;
}

.card {
    display: block;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    padding: 24px;
    text-decoration: none;
    color: inherit;
    transition: transform 0.2s, box-shadow 0.2s;
}

.card:hover {
    transform: translateY(-3px);
    box-shadow: 0 6px 20px rgba(0, 0, 0, 0.12);
}

.card h2 {
    margin: 0 0 8px;
    font-size: 1.25rem;
    color: var(--color-primary);
}

.card p {
    margin: 0;
    color: var(--color-text-light);
    font-size: 0.95rem;
    line-height: 1.5;
}

.card .card-tag {
    display: inline-block;
    margin-top: 12px;
    padding: 3px 10px;
    background-color: #e7f3fe;
    color: #1565c0;
    border-radius: 12px;
    font-size: 0.8rem;
    font-weight: 600;
}

/* --- Responsive (4.3: unified at 640px) --- */
@media (max-width: 640px) {
    header h1 {
        font-size: 1.4rem;
    }

    nav {
        flex-wrap: wrap;
    }

    nav a {
        padding: 0.75rem 1rem;
        font-size: 0.85rem;
        flex: 1;
        text-align: center;
        min-height: 44px;
        display: flex;
        align-items: center;
        justify-content: center;
    }

    main {
        margin: 10px;
        padding: 15px;
    }

    .sim-config {
        flex-direction: column;
        gap: 8px;
    }

    .config-group {
        flex-wrap: wrap;
    }

    [role="radiogroup"] {
        width: 100%;
    }

    .seg-btn {
        padding: 10px 8px;
        font-size: 0.9rem;
        min-height: 44px;
        flex: 1;
        text-align: center;
    }

    .ctrl-btn {
        padding: 12px 20px;
        min-height: 44px;
    }

    .speed-control {
        margin-left: 0;
    }

    .section-nav {
        flex-wrap: wrap;
        gap: 8px;
    }

    .section-nav a {
        padding: 8px 12px;
        min-height: 44px;
        display: inline-flex;
        align-items: center;
    }

    .keyboard-hint {
        display: none;
    }

    .card:hover {
        transform: none;
    }

    .footer-nav {
        flex-direction: column;
        gap: 0;
    }

    .footer-nav a {
        padding: 12px 20px;
        min-height: 44px;
        display: flex;
        align-items: center;
        justify-content: center;
    }
}