*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body{
    height: 100%;
    width: 100%;
}

.center{
    width: 300px;
    height: 200px;
    border: 2px solid black;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}