/* CSS Reset & Base */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --primary-color: #1a365d;
    --primary-light: #2c5282;
    --primary-dark: #0d1b2a;
    --accent-color: #3182ce;
    --success-color: #38a169;
    --warning-color: #d69e2e;
    --danger-color: #e53e3e;
    --background: #f7fafc;
    --card-bg: #ffffff;
    --text-primary: #1a202c;
    --text-secondary: #4a5568;
    --text-muted: #718096;
    --border-color: #e2e8f0;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
}

body {
    font-family: 'Segoe UI', 'Malgun Gothic', sans-serif;
    background: linear-gradient(135deg, var(--primary-dark) 0%, var(--primary-color) 100%);
    min-height: 100vh;
    color: var(--text-primary);
    line-height: 1.6;
}

.container {
    max-width: 900px;
    margin: 0 auto;
    padding: 20px;
}

/* Header */
header {
    text-align: center;
    padding: 40px 20px;
    color: white;
}

header h1 {
    font-size: 2.2rem;
    font-weight: 700;
    margin-bottom: 10px;
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.2);
}

.subtitle {
    font-size: 1.1rem;
    opacity: 0.9;
}

/* Main Content */
main {
    background: var(--card-bg);
    border-radius: 16px;
    box-shadow: var(--shadow-lg);
    padding: 30px;
    margin-bottom: 30px;
}

/* Form Sections */
.form-section {
    margin-bottom: 30px;
    padding-bottom: 25px;
    border-bottom: 1px solid var(--border-color);
}

.form-section:last-of-type {
    border-bottom: none;
    margin-bottom: 20px;
}

.form-section h2 {
    font-size: 1.3rem;
    color: var(--primary-color);
    margin-bottom: 20px;
    padding-left: 10px;
    border-left: 4px solid var(--accent-color);
}

/* Form Groups */
.form-group {
    margin-bottom: 20px;
}

.form-group label {
    display: block;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 8px;
    font-size: 0.95rem;
}

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

.form-group input:focus,
.form-group select:focus {
    outline: none;
    border-color: var(--accent-color);
    box-shadow: 0 0 0 3px rgba(49, 130, 206, 0.2);
}

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

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

/* Select Styling */
select {
    cursor: pointer;
    appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='24' height='24' viewBox='0 0 24 24' fill='none' stroke='%234a5568' stroke-width='2' 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 12px center;
    background-size: 18px;
    padding-right: 45px;
}

optgroup {
    font-weight: 600;
    color: var(--primary-color);
}

/* Buttons */
.button-group {
    display: flex;
    gap: 15px;
    justify-content: center;
    margin-top: 25px;
}

.btn-primary,
.btn-secondary {
    padding: 14px 40px;
    font-size: 1.05rem;
    font-weight: 600;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.3s ease;
}

.btn-primary {
    background: linear-gradient(135deg, var(--accent-color) 0%, var(--primary-color) 100%);
    color: white;
    box-shadow: var(--shadow);
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-secondary {
    background: var(--background);
    color: var(--text-secondary);
    border: 2px solid var(--border-color);
}

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

/* Results Section */
.results-section {
    margin-top: 40px;
    padding-top: 30px;
    border-top: 2px solid var(--border-color);
    animation: fadeIn 0.5s ease;
}

.results-section.hidden {
    display: none;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.results-section h2 {
    font-size: 1.4rem;
    color: var(--primary-color);
    margin-bottom: 25px;
    text-align: center;
}

/* Result Cards */
.result-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 15px;
    margin-bottom: 30px;
}

.result-card {
    background: var(--background);
    border-radius: 12px;
    padding: 20px;
    text-align: center;
    border: 1px solid var(--border-color);
}

.result-card.primary {
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--accent-color) 100%);
    color: white;
    grid-column: span 2;
}

.result-label {
    display: block;
    font-size: 0.85rem;
    margin-bottom: 8px;
    opacity: 0.85;
}

.result-card.primary .result-label {
    color: rgba(255, 255, 255, 0.9);
}

.result-value {
    display: block;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-color);
}

.result-card.primary .result-value {
    color: white;
    font-size: 1.8rem;
}

/* Result Details Table */
.result-details {
    margin-top: 25px;
}

.result-details h3 {
    font-size: 1.1rem;
    color: var(--text-primary);
    margin-bottom: 15px;
}

.detail-table {
    width: 100%;
    border-collapse: collapse;
    background: var(--background);
    border-radius: 8px;
    overflow: hidden;
}

.detail-table td {
    padding: 12px 16px;
    border-bottom: 1px solid var(--border-color);
}

.detail-table tr:last-child td {
    border-bottom: none;
}

.detail-table td:first-child {
    color: var(--text-secondary);
    width: 50%;
}

.detail-table td:last-child {
    font-weight: 600;
    text-align: right;
    color: var(--text-primary);
}

.detail-table tr.highlight {
    background: var(--primary-color);
    color: white;
}

.detail-table tr.highlight td {
    color: white;
    font-weight: 700;
}

/* Formula Info */
.formula-info {
    margin-top: 25px;
    padding: 20px;
    background: #ebf8ff;
    border-radius: 8px;
    border-left: 4px solid var(--accent-color);
}

.formula-info h3 {
    font-size: 1rem;
    color: var(--primary-color);
    margin-bottom: 12px;
}

.formula {
    display: flex;
    flex-direction: column;
    gap: 8px;
    margin-bottom: 12px;
}

.formula code {
    background: white;
    padding: 10px 16px;
    border-radius: 6px;
    font-family: 'Consolas', 'Monaco', monospace;
    font-size: 0.95rem;
    color: var(--primary-color);
}

.note {
    font-size: 0.85rem;
    color: var(--text-muted);
}

/* Footer */
footer {
    text-align: center;
    padding: 20px;
    color: rgba(255, 255, 255, 0.7);
    font-size: 0.9rem;
}

footer p {
    margin-bottom: 5px;
}

/* Responsive Design */
@media (max-width: 768px) {
    header h1 {
        font-size: 1.7rem;
    }

    main {
        padding: 20px;
    }

    .result-card.primary {
        grid-column: span 1;
    }

    .button-group {
        flex-direction: column;
    }

    .btn-primary,
    .btn-secondary {
        width: 100%;
    }
}

/* Input validation styles */
input:invalid:not(:placeholder-shown),
select:invalid:not([value=""]) {
    border-color: var(--danger-color);
}

input:valid:not(:placeholder-shown) {
    border-color: var(--success-color);
}

/* Number input spinner removal */
input[type="number"]::-webkit-inner-spin-button,
input[type="number"]::-webkit-outer-spin-button {
    -webkit-appearance: none;
    margin: 0;
}

input[type="number"] {
    -moz-appearance: textfield;
}