body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    margin: 0;
    padding: 0;
    background-color: #f0f0f0;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

header {
    color: black;
    text-align: center;
}

nav ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
}

nav li {
    margin: 0;
    text-decoration: none;
    color: #000;
    padding: 1em;
    display: block;
    transition: background-color 0.3s ease;
}

nav a {
    text-decoration: none;
    color: #000;
}

nav a:hover {
    background-color: #94a1bc;
}

main {
    flex: 1;
    padding: 1em;
}

input:valid {
    background-color: palegreen;
}

input:invalid {
    background-color: lightpink;
}

table {
    border: 2px solid rgb(140 140 140);
}

th, td {
    border: 1px solid rgb(160 160 160);
}

#error {
    color: darkred;
    text-align: center;
}