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

body {
    font-family: Arial, sans-serif;
    background: #f5f7fb;
    color: #222;
    line-height: 1.6;
}

.header {
    background: linear-gradient(135deg, #4f46e5, #7c3aed);
    color: white;
    padding: 45px 20px;
    text-align: center;
}

.header h1 {
    font-size: 36px;
    margin-bottom: 10px;
}

.header p {
    font-size: 17px;
    opacity: .95;
}

.nav {
    background: #1e1b4b;
    text-align: center;
    padding: 0;
    position: sticky;
    top: 0;
    z-index: 100;
}

.nav a {
    color: #c7d2fe;
    text-decoration: none;
    padding: 14px 22px;
    display: inline-block;
    font-size: 15px;
    transition: .2s;
}

.nav a:hover,
.nav a.active {
    background: #4f46e5;
    color: white;
}

.container {
    max-width: 1100px;
    margin: auto;
    padding: 30px 18px;
}

.intro {
    text-align: center;
    margin-bottom: 30px;
}

.intro h2 {
    font-size: 28px;
    color: #333;
    margin-bottom: 8px;
}

.intro p {
    color: #666;
}

.tricks {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 20px;
}

.card {
    background: white;
    border-radius: 18px;
    padding: 25px;
    box-shadow: 0 8px 25px rgba(0,0,0,.07);
    transition: .25s;
    border: 1px solid #eee;
}

.card:hover {
    transform: translateY(-5px);
    box-shadow: 0 12px 30px rgba(0,0,0,.12);
}

.number {
    width: 42px;
    height: 42px;
    border-radius: 50%;
    background: #4f46e5;
    color: white;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: bold;
    margin-bottom: 15px;
}

.card h3 {
    font-size: 20px;
    margin-bottom: 10px;
    color: #222;
}

.card p {
    color: #666;
    margin-bottom: 12px;
}

.formula {
    background: #f0f2ff;
    padding: 12px 15px;
    border-radius: 10px;
    color: #3730a3;
    font-weight: bold;
    margin: 10px 0;
}

.example {
    background: #f8fafc;
    border-left: 4px solid #7c3aed;
    padding: 12px 15px;
    border-radius: 8px;
}

.answer {
    color: #16a34a;
    font-weight: bold;
}

.practice {
    margin-top: 45px;
    background: linear-gradient(135deg, #111827, #312e81);
    color: white;
    border-radius: 20px;
    padding: 35px 25px;
    text-align: center;
}

.practice h2 {
    margin-bottom: 10px;
}

.practice p {
    opacity: .9;
    margin-bottom: 20px;
}

.questions {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 10px;
    max-width: 700px;
    margin: auto;
}

.question {
    background: white;
    color: #222;
    padding: 12px;
    border-radius: 10px;
    font-weight: bold;
}

footer {
    text-align: center;
    padding: 30px 15px;
    color: #777;
    font-size: 14px;
}

@media (max-width: 850px) {
    .tricks {
        grid-template-columns: repeat(2, 1fr);
    }

    .questions {
        grid-template-columns: repeat(3, 1fr);
    }
}

@media (max-width: 600px) {
    .header {
        padding: 35px 15px;
    }

    .header h1 {
        font-size: 28px;
    }

    .nav a {
        padding: 10px 12px;
        font-size: 13px;
    }

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

    .questions {
        grid-template-columns: repeat(2, 1fr);
    }

    .card {
        padding: 20px;
    }
}