/* style.css */
*, *::before, *::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --primary: #6366f1;
    --primary-dark: #4f46e5;
    --primary-light: #818cf8;
    --primary-glow: rgba(99, 102, 241, 0.25);
    --accent: #f59e0b;
    --accent-light: #fcd34d;
    --success: #10b981;
    --error: #ef4444;

    --bg: #f0f4ff;
    --bg-card: #ffffff;
    --bg-subtle: #f8faff;
    --bg-input: #f1f5f9;

    --text-primary: #0f172a;
    --text-secondary: #475569;
    --text-muted: #94a3b8;

    --border: #e2e8f0;
    --border-focus: var(--primary);

    --shadow-sm: 0 1px 3px rgba(0,0,0,0.06), 0 1px 2px rgba(0,0,0,0.04);
    --shadow-md: 0 4px 12px rgba(0,0,0,0.08), 0 2px 4px rgba(0,0,0,0.04);
    --shadow-lg: 0 10px 30px rgba(0,0,0,0.1), 0 4px 8px rgba(0,0,0,0.05);
    --shadow-xl: 0 20px 50px rgba(0,0,0,0.12), 0 8px 16px rgba(0,0,0,0.06);
    --shadow-glow: 0 0 0 3px var(--primary-glow);

    --radius-sm: 0.5rem;
    --radius-md: 0.75rem;
    --radius-lg: 1rem;
    --radius-xl: 1.5rem;
    --radius-2xl: 2rem;
    --radius-full: 9999px;

    --transition: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 0.35s cubic-bezier(0.4, 0, 0.2, 1);
}

[data-theme="dark"] {
    --bg: #0d1117;
    --bg-card: #161b22;
    --bg-subtle: #1c2333;
    --bg-input: #21262d;

    --text-primary: #f0f6fc;
    --text-secondary: #8b949e;
    --text-muted: #484f58;

    --border: #30363d;
    --border-focus: var(--primary-light);

    --shadow-sm: 0 1px 3px rgba(0,0,0,0.3);
    --shadow-md: 0 4px 12px rgba(0,0,0,0.4);
    --shadow-lg: 0 10px 30px rgba(0,0,0,0.5);
    --shadow-xl: 0 20px 50px rgba(0,0,0,0.6);
}

body {
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
    background: var(--bg);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    transition: background var(--transition-slow), color var(--transition-slow);
}

/* Scrollbar */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: var(--radius-full); }
::-webkit-scrollbar-thumb:hover { background: var(--text-muted); }

.app-wrapper {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 1.5rem;
}

/* ── Header ── */
.site-header {
    background: var(--bg-card);
    border-bottom: 1px solid var(--border);
    position: sticky;
    top: 0;
    z-index: 200;
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    background: rgba(255,255,255,0.85);
    transition: background var(--transition-slow), border-color var(--transition-slow);
}

[data-theme="dark"] .site-header {
    background: rgba(22, 27, 34, 0.9);
}

.header-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.875rem 1.5rem;
    gap: 1rem;
}

.logo-link {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    text-decoration: none;
    color: var(--text-primary);
    font-weight: 800;
    font-size: 1.2rem;
    letter-spacing: -0.02em;
    transition: opacity var(--transition);
}

.logo-link:hover { opacity: 0.8; }

.logo-icon {
    font-size: 1.5rem;
    filter: drop-shadow(0 0 6px rgba(99,102,241,0.5));
}

.logo-highlight { color: var(--primary); }

.header-right {
    display: flex;
    align-items: center;
    gap: 1rem;
}

/* Dark mode toggle */
.theme-toggle {
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius-full);
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    font-size: 1.1rem;
    transition: all var(--transition);
    color: var(--text-secondary);
    flex-shrink: 0;
}

.theme-toggle:hover {
    background: var(--primary);
    color: white;
    border-color: var(--primary);
    transform: rotate(20deg);
}

/* Mobile Menu */
.mobile-menu-toggle {
    display: none;
    background: none;
    border: none;
    cursor: pointer;
    padding: 0.5rem;
    color: var(--text-primary);
    border-radius: var(--radius-sm);
    transition: background var(--transition);
}

.mobile-menu-toggle:hover { background: var(--bg-input); }

.hamburger {
    display: block;
    width: 22px;
    height: 2px;
    background: currentColor;
    position: relative;
    transition: var(--transition);
    border-radius: 2px;
}

.hamburger::before, .hamburger::after {
    content: '';
    position: absolute;
    width: 22px;
    height: 2px;
    background: currentColor;
    border-radius: 2px;
    transition: var(--transition);
}

.hamburger::before { top: -7px; }
.hamburger::after { bottom: -7px; }

.mobile-menu-toggle[aria-expanded="true"] .hamburger { background: transparent; }
.mobile-menu-toggle[aria-expanded="true"] .hamburger::before { transform: rotate(45deg) translate(5px, 5px); }
.mobile-menu-toggle[aria-expanded="true"] .hamburger::after { transform: rotate(-45deg) translate(5px, -5px); }

.main-nav { transition: all var(--transition-slow); }

.nav-list {
    display: flex;
    gap: 0.25rem;
    list-style: none;
}

.nav-link {
    color: var(--text-secondary);
    text-decoration: none;
    font-weight: 500;
    font-size: 0.9rem;
    padding: 0.5rem 0.875rem;
    border-radius: var(--radius-md);
    transition: all var(--transition);
}

.nav-link:hover { color: var(--text-primary); background: var(--bg-input); }
.nav-link.active { color: var(--primary); background: var(--primary-glow); }

/* ── Hero ── */
.hero-section {
    text-align: center;
    padding: 3.5rem 1.5rem 2rem;
}

.hero-badge {
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
    background: var(--primary-glow);
    color: var(--primary);
    font-size: 0.8rem;
    font-weight: 600;
    padding: 0.35rem 0.875rem;
    border-radius: var(--radius-full);
    margin-bottom: 1.25rem;
    border: 1px solid rgba(99,102,241,0.2);
}

.hero-section h1 {
    font-size: clamp(1.75rem, 4vw, 2.75rem);
    font-weight: 800;
    color: var(--text-primary);
    letter-spacing: -0.03em;
    line-height: 1.2;
    margin-bottom: 0.875rem;
}

.hero-section h1 span { color: var(--primary); }

.hero-subtitle {
    font-size: 1.05rem;
    color: var(--text-secondary);
    max-width: 520px;
    margin: 0 auto;
    line-height: 1.7;
}

/* ── Converter Section ── */
.converter-section { padding: 0.5rem 0 3rem; }

.converter-card {
    background: var(--bg-card);
    border-radius: var(--radius-2xl);
    box-shadow: var(--shadow-xl);
    overflow: hidden;
    border: 1px solid var(--border);
    transition: background var(--transition-slow), border-color var(--transition-slow);
}

/* Category Tabs */
.category-tabs-wrapper {
    background: var(--bg-subtle);
    border-bottom: 1px solid var(--border);
    overflow-x: auto;
    scrollbar-width: thin;
    transition: background var(--transition-slow);
}

.category-tabs {
    display: flex;
    gap: 0.25rem;
    padding: 0.75rem 1.25rem;
    min-width: max-content;
}

.cat-btn {
    background: transparent;
    border: none;
    padding: 0.5rem 1rem;
    font-size: 0.82rem;
    font-weight: 600;
    border-radius: var(--radius-full);
    cursor: pointer;
    transition: all var(--transition);
    color: var(--text-secondary);
    font-family: inherit;
    white-space: nowrap;
    display: flex;
    align-items: center;
    gap: 0.35rem;
}

.cat-btn:hover {
    background: var(--bg-card);
    color: var(--text-primary);
    box-shadow: var(--shadow-sm);
}

.cat-btn.active {
    background: var(--primary);
    color: white;
    box-shadow: 0 2px 8px rgba(99,102,241,0.4);
}

.cat-icon { font-size: 0.95rem; }

/* Converter Body */
.converter-body { padding: 2rem; }

.input-group { margin-bottom: 1.5rem; }

.input-label {
    display: block;
    font-weight: 600;
    margin-bottom: 0.5rem;
    color: var(--text-primary);
    font-size: 0.875rem;
}

.input-wrapper {
    position: relative;
    display: flex;
    align-items: center;
}

.input-number {
    width: 100%;
    padding: 1rem 1.25rem;
    font-size: 1.75rem;
    font-weight: 600;
    border: 2px solid var(--border);
    border-radius: var(--radius-lg);
    background: var(--bg-input);
    color: var(--text-primary);
    transition: all var(--transition);
    font-family: 'Inter', monospace;
    letter-spacing: -0.02em;
}

.input-number::placeholder { color: var(--text-muted); }

.input-number:focus {
    outline: none;
    border-color: var(--primary);
    background: var(--bg-card);
    box-shadow: var(--shadow-glow);
}

.input-clear-btn {
    position: absolute;
    right: 1rem;
    background: var(--text-muted);
    border: none;
    color: white;
    width: 22px;
    height: 22px;
    border-radius: 50%;
    font-size: 0.75rem;
    cursor: pointer;
    display: none;
    align-items: center;
    justify-content: center;
    transition: all var(--transition);
    line-height: 1;
}

.input-clear-btn:hover { background: var(--error); transform: scale(1.1); }
.input-clear-btn.visible { display: flex; }

/* Units Row */
.units-row {
    display: grid;
    grid-template-columns: 1fr auto 1fr;
    gap: 0.75rem;
    margin-bottom: 1.5rem;
    align-items: end;
}

.unit-selector-group { display: flex; flex-direction: column; }

.selector-label {
    display: block;
    font-weight: 600;
    margin-bottom: 0.4rem;
    font-size: 0.8rem;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.unit-select {
    width: 100%;
    padding: 0.75rem 1rem;
    border-radius: var(--radius-md);
    border: 2px solid var(--border);
    background: var(--bg-input);
    color: var(--text-primary);
    font-weight: 500;
    font-size: 0.9rem;
    cursor: pointer;
    font-family: inherit;
    transition: all var(--transition);
    appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 24 24' fill='none' stroke='%2394a3b8' stroke-width='2.5' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpolyline points='6 9 12 15 18 9'%3E%3C/polyline%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 0.875rem center;
    padding-right: 2.5rem;
}

.unit-select:focus {
    outline: none;
    border-color: var(--primary);
    background-color: var(--bg-card);
    box-shadow: var(--shadow-glow);
}

.swap-button-wrapper {
    display: flex;
    align-items: center;
    justify-content: center;
    padding-bottom: 0.1rem;
}

.swap-btn {
    background: var(--bg-input);
    border: 2px solid var(--border);
    border-radius: var(--radius-full);
    width: 44px;
    height: 44px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all var(--transition);
    color: var(--text-secondary);
    flex-shrink: 0;
}

.swap-btn:hover {
    background: var(--primary);
    border-color: var(--primary);
    color: white;
    transform: rotate(180deg) scale(1.05);
    box-shadow: 0 4px 12px rgba(99,102,241,0.4);
}

/* Result Card */
.result-card {
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    border-radius: var(--radius-xl);
    padding: 1.75rem;
    text-align: center;
    position: relative;
    overflow: hidden;
    margin-bottom: 1.25rem;
}

.result-card::before {
    content: '';
    position: absolute;
    top: -50%;
    right: -20%;
    width: 200px;
    height: 200px;
    background: rgba(255,255,255,0.05);
    border-radius: 50%;
    pointer-events: none;
}

.result-card::after {
    content: '';
    position: absolute;
    bottom: -30%;
    left: -10%;
    width: 150px;
    height: 150px;
    background: rgba(255,255,255,0.04);
    border-radius: 50%;
    pointer-events: none;
}

.result-header {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    margin-bottom: 0.75rem;
}

.result-label {
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: rgba(255,255,255,0.7);
    font-weight: 600;
}

.result-value {
    font-size: clamp(2rem, 5vw, 3.25rem);
    font-weight: 800;
    color: white;
    letter-spacing: -0.03em;
    line-height: 1.1;
    margin: 0.25rem 0 0.75rem;
    word-break: break-all;
    font-variant-numeric: tabular-nums;
    transition: all 0.15s ease;
}

.result-value.updated {
    animation: resultPop 0.25s cubic-bezier(0.34, 1.56, 0.64, 1);
}

@keyframes resultPop {
    0% { transform: scale(0.95); opacity: 0.7; }
    100% { transform: scale(1); opacity: 1; }
}

.result-detail {
    font-size: 0.85rem;
    color: rgba(255,255,255,0.65);
    font-weight: 500;
}

/* Action Buttons */
.action-buttons {
    display: flex;
    gap: 0.75rem;
}

.btn {
    flex: 1;
    padding: 0.875rem;
    border-radius: var(--radius-md);
    font-weight: 600;
    font-size: 0.875rem;
    cursor: pointer;
    transition: all var(--transition);
    border: none;
    font-family: inherit;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.4rem;
}

.btn:active { transform: scale(0.97); }

.btn-primary {
    background: var(--primary);
    color: white;
    box-shadow: 0 2px 8px rgba(99,102,241,0.35);
}

.btn-primary:hover {
    background: var(--primary-dark);
    box-shadow: 0 4px 16px rgba(99,102,241,0.45);
    transform: translateY(-1px);
}

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

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

/* ── Categories Overview ── */
.categories-overview {
    padding: 4rem 0;
    background: var(--bg-subtle);
    border-top: 1px solid var(--border);
    transition: background var(--transition-slow);
}

.section-header {
    text-align: center;
    margin-bottom: 2.5rem;
}

.section-header h2 {
    font-size: 1.75rem;
    font-weight: 800;
    color: var(--text-primary);
    letter-spacing: -0.02em;
    margin-bottom: 0.5rem;
}

.section-subtitle {
    color: var(--text-secondary);
    font-size: 0.95rem;
}

.categories-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
    gap: 0.875rem;
}

.category-card {
    background: var(--bg-card);
    padding: 1.25rem 1rem;
    border-radius: var(--radius-lg);
    text-align: center;
    font-weight: 600;
    font-size: 0.875rem;
    border: 1px solid var(--border);
    transition: all var(--transition);
    cursor: pointer;
    color: var(--text-secondary);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.5rem;
}

.category-card-icon { font-size: 1.5rem; }

.category-card:hover {
    transform: translateY(-3px);
    box-shadow: var(--shadow-md);
    border-color: var(--primary);
    color: var(--primary);
}

/* ── About Section ── */
.about-section {
    padding: 4rem 0;
    background: var(--bg-card);
    border-top: 1px solid var(--border);
    transition: background var(--transition-slow);
}

.about-section h2 {
    text-align: center;
    font-size: 1.75rem;
    font-weight: 800;
    letter-spacing: -0.02em;
    margin-bottom: 1.5rem;
    color: var(--text-primary);
}

.about-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 1.25rem;
    max-width: 800px;
    margin: 0 auto;
}

.about-feature {
    background: var(--bg-subtle);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 1.5rem;
    text-align: center;
    transition: all var(--transition);
}

.about-feature:hover {
    border-color: var(--primary);
    box-shadow: var(--shadow-sm);
}

.about-feature-icon { font-size: 2rem; margin-bottom: 0.75rem; }

.about-feature h3 {
    font-size: 0.95rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 0.4rem;
}

.about-feature p {
    font-size: 0.82rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

/* ── Footer ── */
.site-footer {
    background: var(--text-primary);
    color: var(--text-muted);
    padding: 3rem 0 1.5rem;
    margin-top: auto;
    transition: background var(--transition-slow);
}

[data-theme="dark"] .site-footer { background: #010409; }

.footer-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 2rem;
    margin-bottom: 2rem;
}

.footer-logo {
    font-size: 1.1rem;
    font-weight: 800;
    color: white;
    letter-spacing: -0.02em;
}

.footer-brand p {
    margin-top: 0.5rem;
    font-size: 0.82rem;
    line-height: 1.6;
}

.footer-links h3, .footer-contact h3 {
    color: white;
    margin-bottom: 1rem;
    font-size: 0.875rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.footer-links ul { list-style: none; }
.footer-links li { margin-bottom: 0.5rem; }

.footer-links a {
    color: var(--text-muted);
    text-decoration: none;
    font-size: 0.875rem;
    transition: color var(--transition);
}

.footer-links a:hover { color: var(--accent); }

.footer-contact p { font-size: 0.875rem; margin-bottom: 0.5rem; }

.footer-bottom {
    text-align: center;
    padding-top: 1.5rem;
    border-top: 1px solid rgba(255,255,255,0.08);
    font-size: 0.8rem;
}
.logo-image {
    width: 32px;
    height: 32px;
    border-radius: 8px;
}

[data-theme="dark"] .logo-image {
    filter: brightness(0) invert(1);
}

/* ── Toast ── */
.toast-notification {
    position: fixed;
    bottom: 2rem;
    left: 50%;
    transform: translateX(-50%) translateY(120%);
    background: var(--text-primary);
    color: white;
    padding: 0.75rem 1.5rem;
    border-radius: var(--radius-full);
    font-size: 0.875rem;
    font-weight: 500;
    opacity: 0;
    transition: all 0.3s cubic-bezier(0.34, 1.56, 0.64, 1);
    pointer-events: none;
    z-index: 1000;
    white-space: nowrap;
    box-shadow: var(--shadow-lg);
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.toast-notification.show {
    transform: translateX(-50%) translateY(0);
    opacity: 1;
}

/* ── Responsive ── */
@media (max-width: 768px) {
    .container { padding: 0 1rem; }

    .mobile-menu-toggle { display: block; }

    .main-nav {
        position: fixed;
        top: 65px;
        left: -100%;
        width: 80%;
        max-width: 280px;
        height: calc(100vh - 65px);
        background: var(--bg-card);
        border-right: 1px solid var(--border);
        transition: left var(--transition-slow);
        box-shadow: var(--shadow-xl);
        z-index: 199;
    }

    .main-nav.open { left: 0; }

    .nav-list {
        flex-direction: column;
        padding: 1.5rem;
        gap: 0.25rem;
    }

    .nav-link { padding: 0.75rem 1rem; }

    .hero-section { padding: 2.5rem 1rem 1.5rem; }

    .converter-body { padding: 1.25rem; }

    .units-row {
        grid-template-columns: 1fr;
        gap: 0.75rem;
    }

    .swap-button-wrapper {
        justify-content: center;
        padding: 0;
    }

    .swap-btn { transform: rotate(90deg); }
    .swap-btn:hover { transform: rotate(270deg) scale(1.05); }

    .result-value { font-size: 2rem; }

    .categories-grid { grid-template-columns: repeat(auto-fill, minmax(130px, 1fr)); }

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

@media (max-width: 480px) {
    .result-value { font-size: 1.75rem; }
    .footer-grid { grid-template-columns: 1fr; }
    .about-grid { grid-template-columns: 1fr; }
    .action-buttons { flex-direction: column; }
}