/* Global Variables & Base */
:root {
    --primary-color: #2563eb;
    --secondary-color: #64748b;
    --bg-light: #f8fafc;
    --bg-dark: #0f172a;
    --card-bg-light: #ffffff;
    --card-bg-dark: #1e293b;
    --text-light: #1e293b;
    --text-dark: #f1f5f9;
}

body {
    margin: 0;
    padding: 0;
    font-family: 'Inter', 'Segoe UI', system-ui, -apple-system, sans-serif;
    background-color: var(--bg-light);
    color: var(--text-light);
    line-height: 1.6;
    transition: background-color 0.3s, color 0.3s;
}

body.dark-mode {
    background-color: var(--bg-dark);
    color: var(--text-dark);
}

/* Header & Global Nav */
header {
    background: rgba(255, 255, 255, 0.8);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid #e2e8f0;
    position: sticky;
    top: 0;
    z-index: 1000;
    padding: 0.5rem 0;
}

body.dark-mode header {
    background: rgba(15, 23, 42, 0.8);
    border-bottom-color: #334155;
}

.nav-container {
    max-width: 1100px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 20px;
}

.logo {
    font-size: 1.25rem;
    font-weight: 800;
    color: var(--primary-color);
    text-decoration: none;
}

.nav-links {
    display: flex;
    gap: 20px;
    align-items: center;
}

.nav-links a {
    text-decoration: none;
    color: var(--secondary-color);
    font-weight: 500;
    font-size: 0.9rem;
    transition: color 0.2s;
}

.nav-links a:hover {
    color: var(--primary-color);
}

/* Top Controls */
.top-controls {
    display: flex;
    gap: 10px;
}

#themeToggleBtn, #langToggleBtn {
    padding: 6px 12px;
    border-radius: 8px;
    border: 1px solid #e2e8f0;
    cursor: pointer;
    background: white;
    font-size: 0.8rem;
    font-weight: 600;
    transition: all 0.2s;
}

body.dark-mode #themeToggleBtn, body.dark-mode #langToggleBtn {
    background: #1e293b;
    color: white;
    border-color: #334155;
}

/* Hero Section */
.hero {
    text-align: center;
    padding: 60px 20px;
    background: linear-gradient(135deg, #eff6ff 0%, #ffffff 100%);
}

body.dark-mode .hero {
    background: linear-gradient(135deg, #1e293b 0%, #0f172a 100%);
}

/* Cards & Layout */
.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 40px 20px;
}

.feature-list {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 25px;
}

.feature-item {
    background: var(--card-bg-light);
    padding: 30px;
    border-radius: 16px;
    border: 1px solid #e2e8f0;
    text-decoration: none;
    color: inherit;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    flex-direction: column;
}

.feature-item:hover {
    transform: translateY(-5px);
    box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
    border-color: var(--primary-color);
}

body.dark-mode .feature-item {
    background: var(--card-bg-dark);
    border-color: #334155;
}

/* Content Sections */
.info-section {
    margin-top: 60px;
    background: white;
    padding: 40px;
    border-radius: 16px;
    border: 1px solid #e2e8f0;
}

body.dark-mode .info-section {
    background: var(--card-bg-dark);
    border-color: #334155;
}

footer {
    text-align: center;
    padding: 60px 20px;
    border-top: 1px solid #e2e8f0;
    margin-top: 80px;
    color: var(--secondary-color);
}

body.dark-mode footer {
    border-top-color: #334155;
}

/* Responsive Design */
@media (max-width: 768px) {
    .nav-container {
        flex-direction: column;
        gap: 15px;
        padding: 15px 20px;
    }

    .nav-links {
        flex-wrap: wrap;
        justify-content: center;
        gap: 10px;
    }

    .hero {
        padding: 40px 20px;
    }

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

    .feature-list {
        grid-template-columns: 1fr;
    }

    .feature-item {
        padding: 20px;
    }

    .info-section {
        padding: 25px;
    }

    .main-layout {
        flex-direction: column;
    }

    .controls, .chart-area {
        min-width: 100% !important;
        width: 100%;
    }

    .input-row, .input-group {
        flex-direction: column;
        align-items: stretch !important;
        gap: 10px !important;
    }

    .input-row input, .input-group input, .input-group select {
        width: 100% !important;
        min-width: unset !important;
    }

    .input-row .unit, .input-with-unit .unit-label {
        margin-left: 0;
        margin-top: 2px;
        font-size: 0.8rem;
    }

    .input-section, .converter-container {
        flex-direction: column;
        align-items: stretch !important;
        padding: 20px !important;
        gap: 15px !important;
        overflow-x: visible !important;
    }

    .results-table th, .results-table td {
        padding: 10px;
        font-size: 0.8rem;
    }

    .info-section div {
        grid-template-columns: 1fr !important;
        gap: 15px !important;
    }
}