body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    display: flex;
    flex-direction: column;
    align-items: center;
    background-color: #f0f0f0;
}
.header {
    width: 100%;
    background-color: #f0f0f0;
    text-align: center;
}
.navbar {
    width: 100%;
    height: 50px;
    background-color: #333;
    overflow: hidden;
    display: flex;
    justify-content: center;
    align-items: center;
}
.navbar a {
    float: left;
    display: block;
    color: #f2f2f2;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    font-size: 20px;
    font-family: Arial, sans-serif;
}
.navbar a:hover {
    background-color: #ddd;
    color: black;
}
.content {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
}
.content .item {
    width: 200px;
    height: 200px;
    border: 1px solid #000;
    margin: 10px;
    display: flex;
    justify-content: center;
    align-items: center;
}
.mainpage {
    width: 50%;
    background-color: #fff; 
    border: 1px solid #000; 
    padding: 10px;
    font-size: 20px;
}