Polisowo centrum Div wewnątrz Div
.contentCentralized {
width: 100%;
height : 200px; //Remove height if you don't want specified height for it
display: flex;
flex-direction: column; //options : row | row-reverse | column | column-reverse
flex-wrap: wrap; //options : flex-start | flex-end | center | baseline | stretch
justify-content: center; //options : start | center | space-between | space-around | space-evenly
align-items: center;
}
<div class="contentCentralized">
<h3>Hello Developers.</h3>
</div>
Beautiful Buzzard