Ratio-maintaining boxes. Got this from http://www.mademyday.de/css-height-equals-width-with-pure-css.html
/* <div class="ratio-box"><div class="ratio-content">content</div></div> */
.ratio-box {
position:relative;
width:100%; /*set the width here*/
}
.ratio-box::before {
content:"";
display:block;
padding-top:75%; /*4:3 ratio*/
padding-top:56.25%; /*16:9 ratio*/
/*(padding percentages refer to the width of the containing block)*/
}
.ratio-content {
position:absolute;
top:0; right:0; bottom:0; left:0;
}