html {

   /*background:url(../img/Bootstrap/fondo3.jpg) no-repeat center center fixed;*/
   background:url(../img/fondo5.jpg) no-repeat center center fixed;
   -webkit-background-size:cover; * navegadores basados en webkit *
   -moz-background-size:cover;  * Mozilla Firefox *
   -o-background-size:cover;  *  Opera *
   background-size:cover;
   background-size:1824px 890px;
}