.box {
position: relative;
width: 50%; /* desired width */
}
.box:before {
content: "";
display: block;
padding-top: 100%; /* initial ratio of 1:1*/
}
.content {
position: absolute;
top: 0;
left: 0;
bottom: 0;
right: 0;
}
/* Other ratios - just apply the desired class to the "box" element */
.ratio2_1:before{
padding-top: 50%;
}
.ratio1_2:before{
padding-top: 200%;
}
.ratio4_3:before{
padding-top: 75%;
}
.ratio16_9:before{
padding-top: 56.25%;
}