#encabezado {margin-left: 15px;}
#uno {position: absolute;top: 50px;left: 10px;width: 300px;}
#dos {position: absolute;top: 50px;left: 320px;width: 300px}
#tres {position: absolute;top: 50px;left: 635px;width: 300px;}
#continuacion {position: absolute;top: 300px;}