<section>
<div>Center</div>
</section>
index.html
html {
background-color: blue;
height: 100vh;
}
html, section {
display: flex;
justify-content: center;
align-items: center;
}
section {
width: 200px;
height: 200px;
background-color: springgreen;
}
div {
background-color: yellow;
color: yellow;
padding: 1rem;
}