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

div {
    position: relative;
    width: 100%;
    height: 100vh;
}

button {
    position: absolute;
    top: 30%;
    left: 50%;
    transform: translate(-50%, 0);
    padding: 5px 10px;
}