:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --secondary-color: #475569;
    --background-color: #f8fafc;
    --card-bg: #ffffff;
    --text-main: #1e293b;
    --text-muted: #64748b;
    --border-color: #e2e8f0;
    --success-color: #10b981;
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --font-sans: 'Inter', system-ui, -apple-system, sans-serif;
}

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

body {
    font-family: var(--font-sans);
    background-color: var(--background-color);
    color: var(--text-main);
    line-height: 1.6;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

/* Header */
header {
    background: var(--card-bg);
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: 100;
}

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

.logo {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-color);
    text-decoration: none;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.nav-links {
    display: flex;
    gap: 2rem;
}

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

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

.mobile-menu-btn {
    display: none;
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    color: var(--text-main);
}

/* Hero Section */
.hero {
    background: linear-gradient(to bottom, var(--card-bg), var(--background-color));
    padding: 4rem 1rem;
    text-align: center;
}

.hero h1 {
    font-size: 2.5rem;
    margin-bottom: 1rem;
    color: var(--text-main);
}

.hero p {
    font-size: 1.125rem;
    color: var(--text-muted);
    max-width: 600px;
    margin: 0 auto 2rem;
}

.btn-cta {
    display: inline-block;
    background: var(--primary-color);
    color: white;
    padding: 0.75rem 1.5rem;
    border-radius: var(--radius-md);
    text-decoration: none;
    font-weight: 600;
    transition: background 0.2s;
}

.btn-cta:hover {
    background: var(--primary-hover);
}

/* Calculator Section */
.calculator-section {
    max-width: 800px;
    margin: -2rem auto 4rem;
    padding: 0 1rem;
    position: relative;
    z-index: 10;
}

.calculator-card {
    background: var(--card-bg);
    padding: 2rem;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-lg);
    border: 1px solid var(--border-color);
}

.input-group {
    margin-bottom: 1.5rem;
}

.input-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
    color: var(--text-main);
}

.input-group input,
.input-group select {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    font-size: 1rem;
    transition: border-color 0.2s;
}

.input-group input:focus,
.input-group select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

.result-box {
    background: #f1f5f9;
    padding: 1.5rem;
    border-radius: var(--radius-md);
    margin-top: 2rem;
    text-align: center;
}

.result-value {
    font-size: 2rem;
    font-weight: 700;
    color: var(--primary-color);
    margin-top: 0.5rem;
}

/* Grid Layout for Tools */
.tools-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 1.5rem;
    max-width: 1200px;
    margin: 2rem auto;
    padding: 0 1rem;
}

.tool-card {
    background: var(--card-bg);
    padding: 1.5rem;
    border-radius: var(--radius-md);
    border: 1px solid var(--border-color);
    transition: transform 0.2s, box-shadow 0.2s;
    text-decoration: none;
    color: inherit;
    display: block;
}

.tool-card:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
    border-color: var(--primary-color);
}

.tool-card h3 {
    margin-bottom: 0.5rem;
    color: var(--text-main);
}

.tool-card p {
    color: var(--text-muted);
    font-size: 0.875rem;
}

/* Content Sections */
.content-section {
    max-width: 800px;
    margin: 4rem auto;
    padding: 0 1rem;
}

.content-section h2 {
    margin-bottom: 1.5rem;
    font-size: 1.8rem;
}

.content-section h3 {
    margin: 1.5rem 0 1rem;
}

.content-section p {
    margin-bottom: 1rem;
}

/* FAQ */
.faq-item {
    border-bottom: 1px solid var(--border-color);
    padding: 1.5rem 0;
}

.faq-question {
    font-weight: 600;
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.faq-answer {
    margin-top: 1rem;
    color: var(--text-muted);
    display: none;
}

.faq-item.active .faq-answer {
    display: block;
}

/* Footer */
footer {
    background: var(--card-bg);
    border-top: 1px solid var(--border-color);
    padding: 3rem 1rem;
    margin-top: auto;
}

.footer-content {
    max-width: 1200px;
    margin: 0 auto;
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 2rem;
}

.footer-section h4 {
    margin-bottom: 1rem;
}

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

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

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

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

.footer-bottom {
    text-align: center;
    margin-top: 3rem;
    padding-top: 2rem;
    border-top: 1px solid var(--border-color);
    color: var(--text-muted);
}

/* Responsive */
@media (max-width: 768px) {
    .nav-links {
        display: none;
        position: absolute;
        top: 100%;
        left: 0;
        right: 0;
        background: var(--card-bg);
        flex-direction: column;
        padding: 1rem;
        border-bottom: 1px solid var(--border-color);
    }
    
    .nav-links.active {
        display: flex;
    }
    
    .mobile-menu-btn {
        display: block;
    }
    
    .hero h1 {
        font-size: 2rem;
    }
}