:root {
    --bg-color: #0f172a;
    --sidebar-bg: #1e293b;
    --card-bg: #1e293b;
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --accent-color: #3b82f6;
    --accent-hover: #2563eb;
    --border-color: #334155;
    --danger: #ef4444;
}

* { box-sizing: border-box; margin: 0; padding: 0; }

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    line-height: 1.5;
}

.app-container {
    display: flex;
    min-height: 100vh;
}

/* Sidebar */
.sidebar {
    width: 280px;
    background-color: var(--sidebar-bg);
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    transition: transform 0.3s ease;
    z-index: 50;
}

.sidebar-header {
    padding: 24px;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    gap: 12px;
}

.sidebar-header h2 { font-size: 1.25rem; font-weight: 600; }
.badge {
    background: rgba(59, 130, 246, 0.2);
    color: #60a5fa;
    padding: 4px 8px;
    border-radius: 999px;
    font-size: 0.75rem;
    font-weight: 600;
}

nav { padding: 16px 0; }

.nav-item {
    display: block;
    padding: 12px 24px;
    color: var(--text-secondary);
    text-decoration: none;
    transition: all 0.2s ease;
    border-left: 3px solid transparent;
}

.nav-item:hover {
    background-color: rgba(255,255,255,0.05);
    color: var(--text-primary);
}

.nav-item.active {
    background-color: rgba(59, 130, 246, 0.1);
    color: var(--accent-color);
    border-left-color: var(--accent-color);
}

/* Main Content */
.content {
    flex: 1;
    padding: 40px;
    overflow-y: auto;
}

.page-section { display: none; animation: fadeIn 0.3s ease; }
.page-section.active { display: block; }

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

header { margin-bottom: 32px; }
header h1 { font-size: 2rem; font-weight: 700; margin-bottom: 8px; }
header p { color: var(--text-secondary); font-size: 1.1rem; }

/* Cards */
.card {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 24px;
    margin-bottom: 24px;
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
}

.card h3 { margin-bottom: 16px; font-size: 1.25rem; }
.card h4 { margin-top: 16px; margin-bottom: 8px; font-size: 1rem; color: var(--text-secondary); }

pre {
    background: #0f172a;
    padding: 16px;
    border-radius: 8px;
    overflow-x: auto;
    border: 1px solid var(--border-color);
    color: #e2e8f0;
    font-size: 0.9rem;
}

/* Grid */
.tools-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 24px;
}

.tool-card {
    cursor: pointer;
    transition: transform 0.2s ease, border-color 0.2s ease;
}

.tool-card:hover {
    transform: translateY(-4px);
    border-color: var(--accent-color);
}

.tool-card .tool-name {
    font-weight: 600;
    font-size: 1.1rem;
    margin-bottom: 8px;
    color: var(--accent-color);
}

/* Forms */
.tool-content {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 24px;
}
@media (max-width: 1024px) {
    .tool-content { grid-template-columns: 1fr; }
}

.form-group { margin-bottom: 16px; }
.form-group label {
    display: block;
    margin-bottom: 6px;
    font-weight: 500;
    color: var(--text-secondary);
    font-size: 0.9rem;
}
.form-group input, .form-group select {
    width: 100%;
    padding: 10px 12px;
    background: var(--bg-color);
    border: 1px solid var(--border-color);
    border-radius: 6px;
    color: var(--text-primary);
    font-size: 1rem;
    transition: border-color 0.2s;
}
.form-group input:focus, .form-group select:focus {
    outline: none;
    border-color: var(--accent-color);
}
.form-group input:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Input with Unit Suffix */
.input-with-unit {
    display: flex;
    align-items: stretch;
}
.input-with-unit input {
    flex: 1;
    border-top-right-radius: 0;
    border-bottom-right-radius: 0;
    min-width: 0;
}
.input-with-unit select, .input-with-unit .unit-label {
    width: auto;
    padding: 0 12px;
    background: var(--sidebar-bg);
    border: 1px solid var(--border-color);
    border-left: none;
    border-top-right-radius: 6px;
    border-bottom-right-radius: 6px;
    color: var(--text-secondary);
    font-size: 0.85rem;
    display: flex;
    align-items: center;
    white-space: nowrap;
}
.input-with-unit select {
    cursor: pointer;
    appearance: none;
    -webkit-appearance: none;
}

/* Conversion Grid */
.conversion-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
}
/* Dual Converter */
.dual-converter {
    display: flex;
    flex-direction: column;
    gap: 20px;
}
.converter-row {
    display: flex;
    flex-direction: column;
    gap: 8px;
}
.converter-row label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}
.converter-equals {
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.5rem;
    color: var(--text-secondary);
    padding: 10px 0;
}

button[type="submit"] {
    width: 100%;
    padding: 12px;
    background: var(--accent-color);
    color: white;
    border: none;
    border-radius: 6px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.2s;
    margin-top: 8px;
}
button[type="submit"]:hover { background: var(--accent-hover); }

/* Results */
.result-value {
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--accent-color);
    margin-bottom: 16px;
    word-break: break-all;
}
.result-explanation { color: var(--text-secondary); }

/* Mobile Navigation Header */
.mobile-nav {
    display: none;
    background-color: var(--sidebar-bg);
    padding: 16px 20px;
    border-bottom: 1px solid var(--border-color);
    align-items: center;
    justify-content: space-between;
}
.mobile-nav h2 { font-size: 1.25rem; font-weight: 600; }
#mobile-menu-btn {
    background: none;
    border: none;
    color: var(--text-primary);
    font-size: 1.5rem;
    cursor: pointer;
}

/* Responsive Overrides */
@media (max-width: 768px) {
    .app-container { flex-direction: column; }
    
    .mobile-nav { display: flex; }
    
    .sidebar {
        position: fixed;
        top: 0;
        left: 0;
        height: 100vh;
        transform: translateX(-100%);
    }
    
    .sidebar.open {
        transform: translateX(0);
        box-shadow: 4px 0 24px rgba(0,0,0,0.5);
    }
    
    .content { padding: 20px; }
    
    .tools-grid { grid-template-columns: 1fr; }
    
    header h1 { font-size: 1.5rem; }
    
    .result-value { font-size: 2rem; }
}