/* ========== CSS RESET & BASE ========== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    /* Light mode colors */
    --bg-primary: #f5f7fa;
    --bg-secondary: #ffffff;
    --text-primary: #1a202c;
    --text-secondary: #4a5568;
    --border-color: #e2e8f0;
    --accent-primary: #3b82f6;
    --accent-hover: #2563eb;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.05);
    --shadow-hover: 0 10px 15px rgba(0, 0, 0, 0.1);
    --success: #10b981;
    --warning: #f59e0b;
    --input-bg: #ffffff;
    --input-border: #cbd5e0;
    --help-text: #718096;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    transition: background-color 0.3s ease, color 0.3s ease;
}

body.dark-mode {
    --bg-primary: #0f172a;
    --bg-secondary: #1e293b;
    --text-primary: #f1f5f9;
    --text-secondary: #cbd5e1;
    --border-color: #334155;
    --accent-primary: #60a5fa;
    --accent-hover: #3b82f6;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.3);
    --shadow-hover: 0 10px 15px rgba(0, 0, 0, 0.5);
    --success: #34d399;
    --warning: #fbbf24;
    --input-bg: #1e293b;
    --input-border: #475569;
    --help-text: #94a3b8;
}

/* ========== LAYOUT ========== */
.container {
    max-width: 1400px;
    margin: 0 auto;
    padding: 20px;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 30px;
    padding-bottom: 20px;
    border-bottom: 2px solid var(--border-color);
}

h1 {
    font-size: 2rem;
    font-weight: 700;
    color: var(--text-primary);
}

/* ========== THEME TOGGLE ========== */
.theme-toggle {
    background: var(--bg-secondary);
    border: 2px solid var(--border-color);
    border-radius: 50px;
    padding: 8px 16px;
    cursor: pointer;
    font-size: 1.2rem;
    display: flex;
    align-items: center;
    gap: 8px;
    transition: all 0.3s ease;
}

.theme-toggle:hover {
    transform: scale(1.05);
    box-shadow: var(--shadow);
}

.icon-moon {
    display: none;
}

body.dark-mode .icon-sun {
    display: none;
}

body.dark-mode .icon-moon {
    display: inline;
}

/* ========== MODE SELECTOR ========== */
.mode-selector {
    display: flex;
    gap: 10px;
    margin-bottom: 30px;
    justify-content: center;
}

.mode-btn {
    padding: 12px 24px;
    background: var(--bg-secondary);
    border: 2px solid var(--border-color);
    border-radius: 8px;
    color: var(--text-primary);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
}

.mode-btn:hover {
    background: var(--accent-primary);
    color: white;
    border-color: var(--accent-primary);
}

.mode-btn.active {
    background: var(--accent-primary);
    color: white;
    border-color: var(--accent-primary);
}

/* ========== CALCULATOR CONTAINER ========== */
.calculator-container {
    display: grid;
    grid-template-columns: 1fr;
    gap: 30px;
}

.calculator-container.compare-mode {
    grid-template-columns: repeat(auto-fit, minmax(450px, 1fr));
}

/* ========== CALCULATOR CARD ========== */
.calculator-card {
    background: var(--bg-secondary);
    border-radius: 16px;
    padding: 30px;
    box-shadow: var(--shadow);
    transition: all 0.3s ease;
    position: relative;
}

.calculator-card:hover {
    box-shadow: var(--shadow-hover);
}

.calculator-card h2 {
    font-size: 1.5rem;
    margin-bottom: 25px;
    color: var(--text-primary);
}

/* ========== FORM GROUPS ========== */
.form-group {
    margin-bottom: 20px;
}

.form-group label {
    display: block;
    margin-bottom: 8px;
    font-weight: 600;
    color: var(--text-primary);
}

.form-group .unit {
    font-weight: 400;
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.form-group input,
.form-group select {
    width: 100%;
    padding: 12px 16px;
    background: var(--input-bg);
    border: 2px solid var(--input-border);
    border-radius: 8px;
    font-size: 1rem;
    color: var(--text-primary);
    transition: all 0.3s ease;
}

.form-group input:focus,
.form-group select:focus {
    outline: none;
    border-color: var(--accent-primary);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

.form-group input::placeholder {
    color: var(--text-secondary);
    opacity: 0.6;
}

.help-text {
    display: block;
    margin-top: 6px;
    font-size: 0.85rem;
    color: var(--help-text);
    font-style: italic;
}

/* ========== RESULTS SECTION ========== */
.results {
    margin-top: 30px;
    padding-top: 25px;
    border-top: 2px solid var(--border-color);
}

.results h3 {
    font-size: 1.25rem;
    margin-bottom: 20px;
    color: var(--text-primary);
}

.result-row {
    display: flex;
    justify-content: space-between;
    padding: 12px 0;
    border-bottom: 1px solid var(--border-color);
}

.result-row:last-child {
    border-bottom: none;
}

.result-label {
    font-weight: 500;
    color: var(--text-secondary);
}

.result-value {
    font-weight: 700;
    color: var(--accent-primary);
}

/* ========== EFFICIENCY BADGE ========== */
.efficiency-badge {
    position: absolute;
    top: 20px;
    right: 20px;
    padding: 8px 16px;
    border-radius: 20px;
    font-weight: 700;
    font-size: 0.9rem;
    display: none;
}

.efficiency-badge.winner {
    display: block;
    background: var(--success);
    color: white;
}

.efficiency-badge.winner::after {
    content: '🏆 More Efficient';
}

/* ========== RESPONSIVE DESIGN ========== */
@media (max-width: 1024px) {
    .calculator-container.compare-mode {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 768px) {
    .container {
        padding: 15px;
    }

    h1 {
        font-size: 1.5rem;
    }

    header {
        flex-direction: column;
        gap: 15px;
        align-items: flex-start;
    }

    .calculator-card {
        padding: 20px;
    }

    .mode-selector {
        flex-direction: column;
    }

    .mode-btn {
        width: 100%;
    }

    .result-row {
        flex-direction: column;
        gap: 5px;
    }
}

@media (max-width: 480px) {
    h1 {
        font-size: 1.3rem;
    }

    .calculator-card h2 {
        font-size: 1.2rem;
    }

    .form-group input,
    .form-group select {
        padding: 10px 12px;
        font-size: 0.95rem;
    }
}