body {
    font-family: Arial, sans-serif;
    margin: 0;
    background-color: #f4f6f8;
    color: #333;
}

nav {
    background-color: #2c3e50;
    padding: 10px;
}

nav a {
    color: white;
    text-decoration: none;
    margin-right: 15px;
    font-weight: bold;
}

nav a:hover {
    text-decoration: underline;
}


h1 {
    text-align: center;
    margin-top: 20px;
}

p {
    text-align: center;
    color: #666;
}


#sigma {
    width: 80%;
    margin: 30px auto;
    border-collapse: collapse;
    background-color: white;
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

#sigma td {
    border: 1px solid #ddd;
    padding: 10px;
    text-align: center;
}


#sigma tr:first-child {
    background-color: #3498db;
    color: white;
    font-weight: bold;
}


#sigma tr:nth-child(even) {
    background-color: #f2f2f2;
}


#sigma tr:hover {
    background-color: #e6f2ff;
}


#sigma tr td[colspan="5"] {
    background-color: #ecf0f1;
    font-style: italic;
}