.mascara {
 display: none; 
 position: fixed; 
 z-index: 1; 
 padding: 2% 0 2% 0; 

 left: 0;
 top: 0;
 width: 100%; 
 height: 100%; 
 overflow: auto; 
 background-color: rgb(0,0,0); 
 background-color: rgba(0,0,0,0.4); 
}
.contenido {
    -webkit-border-radius: 20px;
-moz-border-radius: 20px;
border-radius: 20px;
 background-color: #fff;
 margin: auto;
 padding: 1% 0 1% 0;
 border: 1px solid #888;
 width: 50%;
}
.cerrar {
 color: #aaaaaa;
 float: right; 
 padding: 2% 2% 2% 0;
 font-size: 25px;
 font-weight: bold;
}
.cerrar:hover,
.cerrar:focus {
 color: #000;
 text-decoration: none;
 cursor: pointer;
}