Responsive CSS square with centered text

HTML

<div class="flex">
<div class='square-box'>
    <div class='square-content'><div><span>Aspect ratio 1:1</span></div></div>
</div>
<div class='box'>
    <div class='content'><div><span>Aspect ratio 1:1</span></div></div>
    </div>

CSS

.flex
{
  display:flex;
}
.square-box{
    position: relative;
    width: 50%;
    overflow: hidden;
    background: #4679BD;
}
.square-box:before{
    content: "";
    display: block;
    padding-top: 100%;
}
.square-content{
    position:  absolute;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    color: white;
}
.box
{
  background:#ccc;
  width:100%;
}