body{
 width: 100%;
 height: 100%;
 background-color: #D3D3D3;
 font-size: 12px;
}

.envoltura{
 position: relative;
 float: left;
 width: 400px;
 margin-top: 7%;
 margin-left: 40%;
 margin-right: 40%;

}

.encabezado{
width: 400px;
position: relative;
float: left;
top:0px;
}

.bloque_login{
width: 400px;
height: 100px;
position: relative;
float: left;
top: 40px;
background: #dddddd;
border-radius: 10px 10px 20px 20px;
box-shadow: 10px 10px 5px #aaaaaa;
}

.barra_titulo{
position: relative;
float: left;
top: -18px;
left: -5.5%;
width: 111%;
background: black;
color: white;
text-align: center;
border-radius: 10px 10px 0px 0px;
}

.logo{
width: 100%;
}

img{
 width: 390px;
margin-left: 5px;
}

form{
 width: 90%;
 margin-left: 5%;
 margin-right: 5%;
}

label{
 margin-left: 10%;
}

.boton_ingresar{
 margin-left:40%;
 margin-right:40%;
}