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

body {
    font-family: 'Roboto', sans-serif;
    line-height: 1.6;
    color: #333;
    background-color: #f5f5f5;
}

header {
    background-color: #2c3e50;
    padding: 1rem 0;
    position: fixed;
    width: 100%;
    top: 0;
    z-index: 1000;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

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

.logo {
    color: white;
    font-size: 1.5rem;
    font-weight: 700;
}

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

.nav-links a {
    color: white;
    text-decoration: none;
    font-weight: 500;
    transition: color 0.3s ease;
}

.nav-links a:hover {
    color: #3498db;
}

main {
    margin-top: 80px;
    padding: 2rem;
}

.hero {
    background: linear-gradient(135deg, #3498db, #2c3e50);
    color: white;
    text-align: center;
    padding: 4rem 2rem;
    margin: -2rem -2rem 2rem -2rem;
}

.hero h1 {
    font-size: 2.5rem;
    margin-bottom: 1rem;
}

.content-section {
    max-width: 1200px;
    margin: 0 auto 3rem auto;
    padding: 2rem;
    background: white;
    border-radius: 10px;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

h2 {
    color: #2c3e50;
    margin-bottom: 2rem;
    text-align: center;
}

.concept-card, .technique-card, .problem-card {
    background: #f8f9fa;
    padding: 2rem;
    border-radius: 8px;
    margin-bottom: 2rem;
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
}

.techniques-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
}

.formulas-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
}

.formula-card {
    background: #f8f9fa;
    padding: 2rem;
    border-radius: 8px;
    margin-bottom: 2rem;
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.formula-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

.formula-card h3 {
    color: #2c3e50;
    margin-bottom: 1.5rem;
    text-align: center;
    font-size: 1.3rem;
}

.formula-card .formula {
    background: white;
    padding: 1.5rem;
    border-radius: 8px;
    margin: 1rem 0;
    text-align: center;
    font-size: 1.1rem;
    line-height: 2;
}

.formula-card p {
    margin: 1rem 0;
    color: #666;
    text-align: center;
}

.practice-container {
    display: grid;
    gap: 2rem;
}

button {
    background-color: #3498db;
    color: white;
    border: none;
    padding: 0.8rem 1.5rem;
    border-radius: 5px;
    cursor: pointer;
    font-size: 1rem;
    transition: background-color 0.3s ease;
}

button:hover {
    background-color: #2980b9;
}

.solution {
    margin-top: 1rem;
    padding: 1rem;
    background: #e8f4f8;
    border-radius: 5px;
}

.hidden {
    display: none;
}

.calculator-container {
    max-width: 600px;
    margin: 0 auto;
    text-align: center;
}

#integral-input {
    width: 100%;
    padding: 1rem;
    margin-bottom: 1rem;
    border: 2px solid #ddd;
    border-radius: 5px;
    font-size: 1rem;
}

.result-box {
    margin-top: 1rem;
    padding: 1rem;
    background: #f8f9fa;
    border-radius: 5px;
    min-height: 100px;
}

footer {
    text-align: center;
    padding: 2rem;
    background: #2c3e50;
    color: white;
    margin-top: 3rem;
}

@media (max-width: 768px) {
    nav {
        flex-direction: column;
        gap: 1rem;
    }

    .nav-links {
        flex-direction: column;
        text-align: center;
        gap: 1rem;
    }

    .hero h1 {
        font-size: 2rem;
    }
}