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

:root {
    --bg-primary: #1a1a2e;
    --bg-secondary: #16213e;
    --bg-card: #1f2940;
    --text-primary: #edf2f7;
    --text-secondary: #a0aec0;
    --text-muted: #718096;
    --accent-1: #4fd1c5;
    --accent-2: #f687b3;
    --border: #2d3748;
    --input-bg: #2d3748;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    -webkit-text-size-adjust: 100%;
}

/* Mobile-first base styles */
.container {
    width: 100%;
    padding: 12px;
}

header {
    text-align: center;
    margin-bottom: 10px;
}

header h1 {
    font-size: 1.2rem;
    color: var(--text-primary);
    margin-bottom: 0;
}

header p {
    display: none;
}

/* Input section */
.input-section {
    background: var(--bg-card);
    padding: 12px;
    border-radius: 8px;
    border: 1px solid var(--border);
    margin-bottom: 12px;
}

.input-section h2 {
    display: none;
}

#mortgage-form {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 10px;
}

.form-group {
    display: flex;
    flex-direction: column;
    min-width: 0;
}

.form-group label {
    font-size: 0.75rem;
    font-weight: 500;
    margin-bottom: 3px;
    color: var(--text-secondary);
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.form-group input,
.form-group select {
    width: 100%;
    min-width: 0;
    padding: 10px 8px;
    border: 1px solid var(--border);
    border-radius: 6px;
    font-size: 16px;
    transition: border-color 0.2s;
    -webkit-appearance: none;
    appearance: none;
    background: var(--input-bg);
    color: var(--text-primary);
}

.form-group select {
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'%3E%3Cpath fill='%23a0aec0' d='M6 8L1 3h10z'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 8px center;
    padding-right: 28px;
}

.form-group input:focus,
.form-group select:focus {
    outline: none;
    border-color: var(--accent-1);
}

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

/* Results section */
.results-section {
    animation: fadeIn 0.3s ease;
}

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

/* Charts - side by side */
.charts-row {
    display: flex;
    gap: 10px;
}

.chart-container {
    flex: 1;
    min-width: 0;
    background: var(--bg-card);
    padding: 8px;
    border-radius: 8px;
    border: 1px solid var(--border);
    overflow: hidden;
}

.chart-container h2 {
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin-bottom: 4px;
    text-align: center;
}

#payment-chart,
#equity-chart {
    width: 100%;
    min-height: 180px;
}

/* D3 chart styling */
.chart-container .tick line {
    stroke: var(--border);
}

.chart-container .tick text {
    fill: var(--text-muted);
}

.chart-container .domain {
    stroke: var(--border);
}

/* Summary bar - compact horizontal layout */
.summary-bar {
    display: flex;
    justify-content: space-between;
    background: var(--bg-card);
    padding: 10px 12px;
    border-radius: 8px;
    border: 1px solid var(--border);
    margin-top: 12px;
    gap: 8px;
}

.summary-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    flex: 1;
    min-width: 0;
}

.summary-item .label {
    font-size: 0.65rem;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.3px;
}

.summary-item .value {
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--text-primary);
    white-space: nowrap;
}

/* Tablet and up */
@media (min-width: 600px) {
    .container {
        padding: 20px;
        max-width: 800px;
        margin: 0 auto;
    }

    header {
        margin-bottom: 16px;
    }

    header h1 {
        font-size: 1.75rem;
    }

    header p {
        display: block;
        color: var(--text-secondary);
        font-size: 0.9rem;
    }

    .input-section {
        padding: 20px;
    }

    .input-section h2 {
        display: block;
        font-size: 1rem;
        margin-bottom: 12px;
        color: var(--text-primary);
    }

    #mortgage-form {
        grid-template-columns: repeat(4, 1fr);
        gap: 16px;
    }

    .form-group label {
        font-size: 0.8rem;
    }

    .charts-row {
        gap: 16px;
    }

    .chart-container {
        padding: 16px;
    }

    .chart-container h2 {
        font-size: 0.9rem;
        margin-bottom: 8px;
    }

    #payment-chart,
    #equity-chart {
        min-height: 260px;
    }

    .summary-bar {
        padding: 12px 20px;
    }

    .summary-item .label {
        font-size: 0.7rem;
    }

    .summary-item .value {
        font-size: 1rem;
    }
}

/* Desktop */
@media (min-width: 1024px) {
    .container {
        max-width: 1100px;
    }

    .charts-row {
        gap: 20px;
    }

    .chart-container {
        padding: 20px;
    }

    #payment-chart,
    #equity-chart {
        min-height: 300px;
    }
}