.back {  background-attachment: fixed; background-image:   url(estilos/back_Ini.jpg); background-repeat: no-repeat; background-position: centre top; height: 394px; width: 750px}
.back2 { background-attachment: fixed; background-image:   url(estilos/back_Seg.jpg); background-repeat: no-repeat; background-position: centre top; height: 394px; width: 750px }
.backBoto { background-image:  url(estilos/back_boto.gif); height: 30px; width: 750px }
.backCab { background-image:  url(estilos/back_cab.jpg); height: 161px; width: 750px }
.backSombraA { background-image: url(estilos/sombriA.jpg); background-repeat:  repeat-y; width: 13px }
.backSombraB { background-image: url(estilos/sombriB.jpg); background-repeat:  repeat-y; width: 13px }
.back-Presup { background-attachment: fixed; background-image: url(estilos/back_Pres.jpg); background-repeat: no-repeat; background-position: centre top; height: 394px; width: 750px }
.back-Contacto { background-attachment: fixed; background-image: url(estilos/back_Cont.jpg); background-repeat: no-repeat; background-position: centre top; height: 394px; width: 750px }
.back-Acerca { background-attachment: fixed; background-image: url(estilos/back_Acerca.jpg); background-repeat: no-repeat; background-position: centre top; height: 394px; width: 750px }