body {
    width: 100vw;
    height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
}

.box {
    width: 200px;
    height: 200px;
    background: red;
    margin: 20px;
}

.dark-mode {
    background-color: black;
}

.box1 {
    background-color: blue;
}