/* ===== CSS Variables ===== */
:root {
    /* Light Mode Colors */
    --primary-color: #6366f1;
    --primary-dark: #4f46e5;
    --primary-light: #818cf8;
    --secondary-color: #8b5cf6;
    --success-color: #10b981;
    --danger-color: #ef4444;
    --warning-color: #f59e0b;

    --bg-primary: #ffffff;
    --bg-secondary: #f9fafb;
    --bg-tertiary: #f3f4f6;

    --text-primary: #111827;
    --text-secondary: #6b7280;
    --text-tertiary: #9ca3af;

    --border-color: #e5e7eb;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.07);
    --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px rgba(0, 0, 0, 0.15);

    --transition: all 0.3s ease;
    --radius: 12px;
    --radius-sm: 8px;
    --radius-lg: 16px;
}

[data-theme="dark"] {
    /* Dark Mode Colors */
    --bg-primary: #1f2937;
    --bg-secondary: #111827;
    --bg-tertiary: #374151;

    --text-primary: #f9fafb;
    --text-secondary: #d1d5db;
    --text-tertiary: #9ca3af;

    --border-color: #374151;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.5);
    --shadow-xl: 0 20px 25px rgba(0, 0, 0, 0.6);
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg-secondary);
    color: var(--text-primary);
    line-height: 1.6;
    transition: var(--transition);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

main {
    flex: 1;
    padding-top: 80px;
}

/* ===== Navigation Bar ===== */
.navbar {
    background: var(--bg-primary);
    border-bottom: 1px solid var(--border-color);
    box-shadow: var(--shadow-sm);
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
    transition: var(--transition);
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 1rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-color);
}

.logo i {
    font-size: 1.75rem;
}

.nav-links {
    display: flex;
    list-style: none;
    gap: 2rem;
}

.nav-links a {
    text-decoration: none;
    color: var(--text-secondary);
    font-weight: 500;
    transition: var(--transition);
    position: relative;
    padding: 0.5rem 0;
}

.nav-links a::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--primary-color);
    transition: var(--transition);
}

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

.nav-links a:hover::after,
.nav-links a.active::after {
    width: 100%;
}

.theme-toggle {
    background: var(--bg-tertiary);
    border: none;
    width: 45px;
    height: 45px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: var(--transition);
    color: var(--text-primary);
    font-size: 1.2rem;
}

.theme-toggle:hover {
    background: var(--primary-color);
    color: white;
    transform: rotate(180deg);
}

/* ===== Container & Layout ===== */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem;
}

.section {
    display: none;
    animation: fadeIn 0.5s ease;
}

.section.active {
    display: block;
}

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

/* ===== Cards ===== */
.card {
    background: var(--bg-primary);
    border-radius: var(--radius);
    padding: 2rem;
    box-shadow: var(--shadow-md);
    transition: var(--transition);
    border: 1px solid var(--border-color);
}

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

.card-title {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 1.5rem;
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

.card-title i {
    color: var(--primary-color);
}

/* ===== Calculator Grid ===== */
.calculator-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
    margin-bottom: 2rem;
}

/* ===== Input Styles ===== */
.input-group {
    margin-bottom: 1.5rem;
}

.input-row {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
}

label {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-weight: 600;
    color: var(--text-secondary);
    margin-bottom: 0.5rem;
    font-size: 0.9rem;
}

label i {
    color: var(--primary-color);
    font-size: 0.9rem;
}

input,
select,
textarea {
    width: 100%;
    padding: 0.875rem 1rem;
    border: 2px solid var(--border-color);
    border-radius: var(--radius-sm);
    font-size: 1rem;
    background: var(--bg-secondary);
    color: var(--text-primary);
    transition: var(--transition);
    outline: none;
}

input:focus,
select:focus,
textarea:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

input.error {
    border-color: var(--danger-color);
}

.error-message {
    color: var(--danger-color);
    font-size: 0.8rem;
    margin-top: 0.25rem;
    display: none;
}

.error-message.show {
    display: block;
}

/* ===== Buttons ===== */
.button-group {
    display: flex;
    gap: 1rem;
    margin-top: 2rem;
}

.btn {
    padding: 0.875rem 1.5rem;
    border: none;
    border-radius: var(--radius-sm);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    flex: 1;
}

.btn-primary {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
}

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

.btn-secondary {
    background: var(--bg-tertiary);
    color: var(--text-primary);
}

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

.btn-download {
    width: 100%;
    margin-top: 1.5rem;
    background: var(--success-color);
    color: white;
}

.btn-download:hover {
    background: #059669;
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-danger {
    background: var(--danger-color);
    color: white;
}

.btn-danger:hover {
    background: #dc2626;
}

.btn-sm {
    padding: 0.5rem 1rem;
    font-size: 0.875rem;
}

/* ===== Results Card ===== */
.results-card {
    animation: slideInRight 0.5s ease;
}

@keyframes slideInRight {
    from {
        opacity: 0;
        transform: translateX(30px);
    }
    to {
        opacity: 1;
        transform: translateX(0);
    }
}

.results-grid {
    display: grid;
    gap: 1rem;
}

.result-item {
    display: flex;
    align-items: center;
    gap: 1rem;
    padding: 1rem;
    background: var(--bg-secondary);
    border-radius: var(--radius-sm);
    transition: var(--transition);
}

.result-item:hover {
    background: var(--bg-tertiary);
    transform: translateX(5px);
}

.result-item.highlight {
    background: linear-gradient(135deg, rgba(99, 102, 241, 0.1), rgba(139, 92, 246, 0.1));
    border: 2px solid var(--primary-color);
}

.result-icon {
    width: 50px;
    height: 50px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--primary-color);
    color: white;
    font-size: 1.25rem;
}

.result-item.highlight .result-icon {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0%, 100% {
        transform: scale(1);
    }
    50% {
        transform: scale(1.05);
    }
}

.result-info {
    flex: 1;
    display: flex;
    flex-direction: column;
}

.result-label {
    font-size: 0.875rem;
    color: var(--text-secondary);
    font-weight: 500;
}

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

.result-value.positive {
    color: var(--success-color);
}

.result-value.negative {
    color: var(--danger-color);
}

/* ===== Charts Container ===== */
.charts-container {
    display: none;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
    margin-bottom: 2rem;
    animation: fadeIn 0.5s ease;
}

.charts-container.show {
    display: grid;
}

.chart-card {
    padding: 1.5rem;
}

.chart-title {
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 1rem;
    text-align: center;
}

/* ===== History Card ===== */
.history-card {
    margin-top: 2rem;
}

.history-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1.5rem;
}

.history-list {
    max-height: 400px;
    overflow-y: auto;
}

.history-list::-webkit-scrollbar {
    width: 8px;
}

.history-list::-webkit-scrollbar-track {
    background: var(--bg-secondary);
    border-radius: 4px;
}

.history-list::-webkit-scrollbar-thumb {
    background: var(--primary-color);
    border-radius: 4px;
}

.history-item {
    padding: 1.25rem;
    background: var(--bg-secondary);
    border-radius: var(--radius-sm);
    margin-bottom: 1rem;
    border-left: 4px solid var(--primary-color);
    transition: var(--transition);
    cursor: pointer;
}

.history-item:hover {
    background: var(--bg-tertiary);
    transform: translateX(5px);
}

.history-date {
    font-size: 0.75rem;
    color: var(--text-tertiary);
    margin-bottom: 0.5rem;
}

.history-details {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 0.75rem;
}

.history-detail {
    font-size: 0.875rem;
}

.history-detail strong {
    color: var(--primary-color);
}

.empty-state {
    text-align: center;
    color: var(--text-tertiary);
    padding: 3rem;
    font-style: italic;
}

/* ===== About & Contact Sections ===== */
.content-card {
    background: var(--bg-primary);
    border-radius: var(--radius);
    padding: 3rem;
    box-shadow: var(--shadow-md);
    animation: fadeIn 0.5s ease;
}

.page-title {
    font-size: 2.5rem;
    font-weight: 800;
    color: var(--text-primary);
    margin-bottom: 2rem;
    display: flex;
    align-items: center;
    gap: 1rem;
}

.page-title i {
    color: var(--primary-color);
}

.about-content p,
.contact-content p {
    font-size: 1.125rem;
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
    line-height: 1.8;
}

.about-content h2 {
    font-size: 1.75rem;
    color: var(--text-primary);
    margin: 2rem 0 1rem;
}

.features-list {
    list-style: none;
    display: grid;
    gap: 1rem;
    margin: 1.5rem 0;
}

.features-list li {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    font-size: 1.1rem;
    color: var(--text-secondary);
}

.features-list i {
    color: var(--success-color);
    font-size: 1.25rem;
}

.stats-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 2rem;
    margin-top: 3rem;
}

.stat-card {
    text-align: center;
    padding: 2rem;
    background: var(--bg-secondary);
    border-radius: var(--radius);
    transition: var(--transition);
}

.stat-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-lg);
}

.stat-card i {
    font-size: 3rem;
    color: var(--primary-color);
    margin-bottom: 1rem;
}

.stat-card h3 {
    font-size: 2.5rem;
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

.stat-card p {
    color: var(--text-secondary);
    font-size: 1rem;
}

/* ===== Contact Form ===== */
.contact-form {
    margin: 2rem 0;
    max-width: 600px;
}

.contact-info {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
    margin-top: 3rem;
}

.contact-item {
    display: flex;
    gap: 1rem;
    align-items: flex-start;
}

.contact-item i {
    font-size: 1.5rem;
    color: var(--primary-color);
    margin-top: 0.25rem;
}

.contact-item h4 {
    font-size: 1.125rem;
    color: var(--text-primary);
    margin-bottom: 0.25rem;
}

.contact-item p {
    font-size: 0.95rem;
    color: var(--text-secondary);
    margin: 0;
}

/* ===== Footer ===== */
.footer {
    background: var(--bg-primary);
    border-top: 1px solid var(--border-color);
    margin-top: 4rem;
    padding: 3rem 0 1rem;
}

.footer-content {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 2rem;
    margin-bottom: 2rem;
}

.footer-section h4 {
    color: var(--text-primary);
    margin-bottom: 1rem;
    font-size: 1.125rem;
}

.footer-section p {
    color: var(--text-secondary);
    font-size: 0.95rem;
}

.footer-section ul {
    list-style: none;
}

.footer-section ul li {
    margin-bottom: 0.5rem;
}

.footer-section a {
    color: var(--text-secondary);
    text-decoration: none;
    transition: var(--transition);
}

.footer-section a:hover {
    color: var(--primary-color);
}

.social-links {
    display: flex;
    gap: 1rem;
}

.social-links a {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    background: var(--bg-secondary);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.25rem;
    transition: var(--transition);
}

.social-links a:hover {
    background: var(--primary-color);
    color: white;
    transform: translateY(-3px);
}

.footer-bottom {
    text-align: center;
    padding-top: 2rem;
    border-top: 1px solid var(--border-color);
    color: var(--text-tertiary);
}

/* ===== Responsive Design ===== */
@media (max-width: 1024px) {
    .calculator-grid,
    .charts-container {
        grid-template-columns: 1fr;
    }

    .stats-grid {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 768px) {
    .nav-container {
        padding: 1rem;
    }

    .nav-links {
        gap: 1rem;
    }

    .container {
        padding: 1rem;
    }

    .card {
        padding: 1.5rem;
    }

    .input-row {
        grid-template-columns: 1fr;
    }

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

    .page-title {
        font-size: 2rem;
    }

    .footer-content {
        grid-template-columns: 1fr;
    }

    .content-card {
        padding: 2rem 1.5rem;
    }
}

@media (max-width: 480px) {
    .logo span {
        display: none;
    }

    .nav-links {
        font-size: 0.875rem;
        gap: 0.75rem;
    }

    .card-title {
        font-size: 1.25rem;
    }

    .result-value {
        font-size: 1.25rem;
    }

    .page-title {
        font-size: 1.5rem;
    }
}