box-sizing: content-box;
:after { height: 100%; }
box-sizing: content-box;
:after { padding-bottom: 100%; }
box-sizing: border-box;
:after { padding-bottom: 100%; }
box-sizing: border-box;
.box__inner { padding-bottom: 100%; }
box-sizing: border-box;
:after { aspect-ratio: 1 / 1 }
box-sizing: border-box;
.box__inner { aspect-ratio: 1 / 1 }