/* ============================================
   OpenChess Build Guide — Stylesheet
   ============================================ */

:root {
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-card: #1c2128;
    --bg-card-hover: #21262d;
    --text-primary: #e6edf3;
    --text-secondary: #8b949e;
    --text-muted: #6e7681;
    --accent: #58a6ff;
    --accent-hover: #79b8ff;
    --accent-glow: rgba(88, 166, 255, 0.15);
    --green: #3fb950;
    --yellow: #d29922;
    --red: #f85149;
    --purple: #bc8cff;
    --border: #30363d;
    --sidebar-width: 260px;
    --topbar-height: 56px;
    --radius: 12px;
    --radius-sm: 8px;
}

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

html {
    scroll-behavior: smooth;
    scroll-padding-top: 80px;
    font-size: 16px;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.7;
    overflow-x: hidden;
}

a {
    color: var(--accent);
    text-decoration: none;
    transition: color 0.2s;
}

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

img {
    max-width: 100%;
    height: auto;
    display: block;
}

code,
kbd {
    font-family: 'SF Mono', 'Fira Code', 'Fira Mono', monospace;
    background: var(--bg-secondary);
    padding: 0.15em 0.4em;
    border-radius: 4px;
    font-size: 0.9em;
    border: 1px solid var(--border);
}

kbd {
    box-shadow: 0 1px 0 var(--border);
}

/* ---- Sidebar ---- */
#sidebar {
    position: fixed;
    top: 0;
    left: 0;
    width: var(--sidebar-width);
    height: 100vh;
    background: var(--bg-secondary);
    border-right: 1px solid var(--border);
    z-index: 100;
    overflow-y: auto;
    transition: transform 0.3s ease;
}

.sidebar-header {
    padding: 1.5rem;
    border-bottom: 1px solid var(--border);
}

.sidebar-header h2 {
    font-size: 1.3rem;
    font-weight: 700;
    margin-bottom: 0.2rem;
}

.sidebar-subtitle {
    font-size: 0.8rem;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.1em;
}

.nav-links {
    list-style: none;
    padding: 0.75rem 0;
}

.nav-links li a {
    display: block;
    padding: 0.55rem 1.5rem;
    color: var(--text-secondary);
    font-size: 0.875rem;
    font-weight: 400;
    transition: all 0.2s;
    border-left: 3px solid transparent;
}

.nav-links li a:hover {
    color: var(--text-primary);
    background: var(--accent-glow);
}

.nav-links li a.active {
    color: var(--accent);
    border-left-color: var(--accent);
    background: var(--accent-glow);
    font-weight: 500;
}

/* ---- Mobile Topbar ---- */
#mobile-topbar {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: var(--topbar-height);
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border);
    z-index: 99;
    align-items: center;
    padding: 0 1rem;
    gap: 0.75rem;
    font-weight: 600;
    font-size: 0.95rem;
}

#menu-toggle {
    background: none;
    border: 1px solid var(--border);
    color: var(--text-primary);
    font-size: 1.3rem;
    padding: 0.3rem 0.6rem;
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: background 0.2s;
}

#menu-toggle:hover {
    background: var(--bg-card);
}

/* ---- Main Content ---- */
#content {
    margin-left: var(--sidebar-width);
    min-height: 100vh;
}

/* ---- Hero ---- */
.hero-section {
    display: flex;
    align-items: center;
    gap: 3rem;
    padding: 5rem 4rem;
    min-height: 80vh;
    background: linear-gradient(135deg, var(--bg-primary) 0%, #0f1923 100%);
}

.hero-text {
    flex: 1;
}

.hero-text h1 {
    font-size: 3rem;
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: 1.2rem;
}

.accent {
    background: linear-gradient(135deg, var(--accent), var(--purple));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-description {
    font-size: 1.15rem;
    color: var(--text-secondary);
    line-height: 1.8;
    margin-bottom: 2rem;
    max-width: 560px;
}

.hero-image {
    flex: 1;
    max-width: 480px;
}

.hero-image img {
    border-radius: var(--radius);
    border: 1px solid var(--border);
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.4);
}

.btn-primary,
.btn-secondary {
    display: inline-block;
    padding: 0.75rem 1.75rem;
    border-radius: var(--radius-sm);
    font-weight: 600;
    font-size: 0.95rem;
    transition: all 0.2s;
    margin-right: 0.75rem;
}

.btn-primary {
    background: var(--accent);
    color: #fff;
}

.btn-primary:hover {
    background: var(--accent-hover);
    color: #fff;
    transform: translateY(-1px);
    box-shadow: 0 4px 20px rgba(88, 166, 255, 0.3);
}

.btn-secondary {
    background: transparent;
    color: var(--text-secondary);
    border: 1px solid var(--border);
}

.btn-secondary:hover {
    color: var(--text-primary);
    border-color: var(--text-muted);
}

/* ---- Sections ---- */
.section {
    padding: 4rem;
    border-top: 1px solid var(--border);
}

.section-title {
    font-size: 2rem;
    font-weight: 700;
    margin-bottom: 0.75rem;
}

.section-intro {
    font-size: 1.05rem;
    color: var(--text-secondary);
    margin-bottom: 2.5rem;
}

/* ---- Step Cards ---- */
.step-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 2rem;
    margin-bottom: 2rem;
    position: relative;
    transition: border-color 0.2s;
}

.step-card:hover {
    border-color: var(--text-muted);
}

.step-card h3 {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
}

.step-card>p {
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
}

/* ---- Images ---- */
.image-container {
    position: relative;
    overflow: hidden;
    border-radius: var(--radius-sm);
    border: 1px solid var(--border);
    background: var(--bg-secondary);
}

.image-container img {
    width: 100%;
    max-height: 60vh;
    object-fit: contain;
    transition: transform 0.3s ease;
    cursor: zoom-in;
}

.image-container img:hover {
    transform: scale(1.02);
}

.image-caption {
    display: block;
    text-align: center;
    font-size: 0.8rem;
    color: var(--text-muted);
    padding: 0.5rem;
    background: var(--bg-card);
    border-top: 1px solid var(--border);
}

.image-row {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.5rem;
}

/* ---- Materials Grid ---- */
.materials-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 1.25rem;
    margin-bottom: 2rem;
}

.material-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 1.5rem;
    transition: all 0.2s;
}

.material-card:hover {
    border-color: var(--accent);
    background: var(--bg-card-hover);
}

.material-icon {
    font-size: 1.5rem;
    margin-bottom: 0.75rem;
}

.material-card h3 {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 0.4rem;
}

.material-card p {
    font-size: 0.875rem;
    color: var(--text-secondary);
}

/* ---- Info Box ---- */
.info-box {
    background: var(--accent-glow);
    border: 1px solid rgba(88, 166, 255, 0.2);
    border-radius: var(--radius-sm);
    padding: 1.25rem 1.5rem;
    font-size: 0.95rem;
    color: var(--text-secondary);
}

.info-box strong {
    color: var(--accent);
}

/* ---- Software Steps ---- */
.software-steps h3 {
    font-size: 1.1rem;
    color: var(--accent);
    margin-top: 1.75rem;
    margin-bottom: 0.5rem;
}

.software-steps h3:first-child {
    margin-top: 0;
}

.software-steps ul {
    margin-left: 1.5rem;
    color: var(--text-secondary);
}

.software-steps li {
    margin-bottom: 0.4rem;
}

.software-steps ul ul {
    margin-top: 0.4rem;
}

/* ---- Footer ---- */
footer {
    text-align: center;
    padding: 3rem 2rem;
    border-top: 1px solid var(--border);
    color: var(--text-muted);
    font-size: 0.875rem;
}

/* ---- Zoom Modal ---- */
.zoom-modal {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.92);
    z-index: 1000;
    cursor: default;
    justify-content: center;
    align-items: center;
    padding: 2rem;
}

.zoom-modal.active {
    display: flex;
}

.zoom-modal img {
    max-width: 90vw;
    max-height: 90vh;
    border-radius: var(--radius-sm);
    box-shadow: 0 20px 80px rgba(0, 0, 0, 0.5);
    object-fit: contain;
    transform-origin: center center;
    transition: transform 0.15s ease;
    cursor: default;
}

.zoom-modal img.zoomed {
    cursor: grab;
}

.zoom-modal img.zoomed.dragging {
    cursor: grabbing;
}

.zoom-close {
    position: absolute;
    top: 1.5rem;
    right: 2rem;
    font-size: 2.5rem;
    color: var(--text-secondary);
    cursor: pointer;
    transition: color 0.2s;
    line-height: 1;
    z-index: 1001;
}

.zoom-close:hover {
    color: var(--text-primary);
}

/* Navigation arrows */
.zoom-nav {
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
    background: rgba(255, 255, 255, 0.1);
    border: 1px solid rgba(255, 255, 255, 0.15);
    color: var(--text-secondary);
    font-size: 1.8rem;
    width: 48px;
    height: 48px;
    border-radius: 50%;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.2s;
    z-index: 1001;
    user-select: none;
    -webkit-user-select: none;
}

.zoom-nav:hover {
    background: rgba(255, 255, 255, 0.2);
    color: var(--text-primary);
}

.zoom-nav:active {
    transform: translateY(-50%) scale(0.95);
}

.zoom-nav.disabled {
    opacity: 0.2;
    pointer-events: none;
}

.zoom-prev {
    left: 1.25rem;
}

.zoom-next {
    right: 1.25rem;
}

/* Counter */
.zoom-counter {
    position: absolute;
    bottom: 1.25rem;
    left: 50%;
    transform: translateX(-50%);
    background: rgba(0, 0, 0, 0.6);
    border: 1px solid rgba(255, 255, 255, 0.1);
    color: var(--text-secondary);
    font-size: 0.85rem;
    font-weight: 500;
    padding: 0.35rem 1rem;
    border-radius: 20px;
    z-index: 1001;
    letter-spacing: 0.05em;
    user-select: none;
    -webkit-user-select: none;
}

/* ---- Scrollbar ---- */
::-webkit-scrollbar {
    width: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-primary);
}

::-webkit-scrollbar-thumb {
    background: var(--border);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--text-muted);
}

/* ============================================
   Responsive
   ============================================ */
@media (max-width: 1024px) {
    .hero-section {
        flex-direction: column;
        padding: 3rem 2rem;
        min-height: auto;
        text-align: center;
    }

    .hero-text h1 {
        font-size: 2.2rem;
    }

    .hero-description {
        margin: 0 auto 2rem;
    }

    .hero-image {
        max-width: 360px;
    }

    .section {
        padding: 3rem 2rem;
    }
}

@media (max-width: 768px) {
    #sidebar {
        transform: translateX(-100%);
    }

    #sidebar.open {
        transform: translateX(0);
        box-shadow: 4px 0 20px rgba(0, 0, 0, 0.5);
    }

    #mobile-topbar {
        display: flex;
    }

    #content {
        margin-left: 0;
        padding-top: var(--topbar-height);
    }

    html {
        scroll-padding-top: calc(var(--topbar-height) + 16px);
    }

    .hero-text h1 {
        font-size: 1.8rem;
    }

    .hero-section {
        padding: 2rem 1.25rem;
    }

    .section {
        padding: 2rem 1.25rem;
    }

    .step-card {
        padding: 1.5rem;
    }

    .image-row {
        grid-template-columns: 1fr;
    }

    .materials-grid {
        grid-template-columns: 1fr 1fr;
    }
}

@media (max-width: 480px) {
    .materials-grid {
        grid-template-columns: 1fr;
    }
}

/* ---- Floating Step Navigator ---- */
.step-nav {
    position: fixed;
    bottom: 1.5rem;
    right: 1.5rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 28px;
    padding: 0.4rem 0.5rem;
    z-index: 90;
    box-shadow: 0 4px 24px rgba(0, 0, 0, 0.4);
    transition: opacity 0.3s, transform 0.3s;
}

.step-nav.hidden {
    opacity: 0;
    transform: translateY(20px);
    pointer-events: none;
}

.step-nav-btn {
    background: rgba(255, 255, 255, 0.08);
    border: 1px solid var(--border);
    color: var(--text-secondary);
    font-size: 1.4rem;
    width: 38px;
    height: 38px;
    border-radius: 50%;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.2s;
    user-select: none;
    -webkit-user-select: none;
    line-height: 1;
}

.step-nav-btn:hover {
    background: rgba(255, 255, 255, 0.15);
    color: var(--text-primary);
}

.step-nav-btn:active {
    transform: scale(0.93);
}

.step-nav-btn.disabled {
    opacity: 0.25;
    pointer-events: none;
}

.step-nav-counter {
    color: var(--text-secondary);
    font-size: 0.8rem;
    font-weight: 500;
    min-width: 52px;
    text-align: center;
    letter-spacing: 0.03em;
    user-select: none;
    -webkit-user-select: none;
}