body {
    margin: 0;
    font-family: Arial, sans-serif;
    display: flex;
    flex-direction: column;
    height: 100vh;
}
.box {
    flex: 1;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 20px;
    font-weight: bold;
    color: white;
}
.box1 { background-color: green; }
.box2 { background-color: white; color: black;}
.box3 { background-color: red; }