<div id = "contenido"></div> <div id = "capa"></div>
body{ margin: 0; } #contenido{ width: 30em; height: 17.5em; background: aquamarine; border: .1em lightgray solid; } #capa{ width: 30.15em; height: 0; background: black; opacity: .75; animation: cortina 2.5s; -webkit-animation: cortina 2.5s; -moz-animation: cortina 2.5s; position: absolute; top: 0; } @keyframes cortina{ from{ height: 17.5em; } to{ height: 0; } } @-webkit-keyframes cortina{ from{ height: 17.5em; } to{ height: 0; } } @-moz-keyframes cortina{ from{ height: 17.5em; } to{ height: 0; } }