body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    margin: 0;
    color: #333;
    background-color: #f4f4f4;
}

header {
    background: #2c3e50;
    color: #fff;
    padding: 1.5rem 0;
    text-align: center;
}

.logo {
    font-size: 1.8rem;
    font-weight: bold;
    text-transform: uppercase;
    letter-spacing: 2px;
}

nav {
    background: #34495e;
    display: flex;
    justify-content: center;
    padding: 0.5rem;
    position: sticky;
    top: 0;
    flex-wrap: wrap;
}

nav a {
    color: white;
    text-decoration: none;
    padding: 0.5rem 1.2rem;
    margin: 2px 5px;
    border-radius: 4px;
    font-weight: 500;
}

nav a:hover {
    background: #1abc9c;
}

.container {
    max-width: 900px;
    margin: 30px auto;
    padding: 30px;
    background: white;
    box-shadow: 0 4px 15px rgba(0,0,0,0.1);
    border-radius: 8px;
}

h1 { color: #2c3e50; border-bottom: 2px solid #1abc9c; padding-bottom: 10px; }

.problem-card {
    border-left: 5px solid #1abc9c;
    background: #ecf0f1;
    padding: 20px;
    margin: 20px 0;
    border-radius: 0 4px 4px 0;
}

p { margin-bottom: 20px; text-align: justify; }