Practica botón enviar

header{
    background-color: #bbbbbb;
    padding: 20px 0;

}
.caja {
    width: 940px;
    position: relative;
    margin:  0 auto;

}
nav {
    position: absolute;
    top: 100px;
    right: 0;
}
nav li{
    display: inline;
    margin: 0 0 0 15px;
}

nav a {
    text-transform: uppercase;
    color: #000000;
    font-weight: bold;
    font-size: 22px;
    text-decoration: none;
}
nav a:hover {
    color: #c78c19;
    text-decoration: underline;
}
.producto {

    width: 940px;
    margin: 0 auto;
    padding: 50px;

}
.producto li{
    display: inline-block;
    text-align: center;
    width: 30%;
    vertical-align: top;
    margin: 0 1.5%;
    padding: 30px 20px;
    box-sizing: border-box;
    border: 6px solid #000000;
    border-radius:  15px;
}
.producto li:hover{
    border-color: #c78c19;

}
.producto li:active{
    border-color: aqua;
}
.producto h2 {
    font-size: 30px;
    font-weight: bold;    
} 
.producto li:hover h2 {
    font-size: 35px;

}  
.producto-descripcion {
    font-size: 18px;
}
.producto-precio {
    font-size: 20 px;
    font-weight: bold;
    margin-top: 10px;
}
footer {
    text-align: center;
    background:url(imagenes/bg.jpg);
    padding: 40px;
}
.copyright {
    color: #ffffff;
    font-size: 13px;
    margin: 20px;
}
main {
    width: 940px;
    margin: 0 auto;
}
form {
    margin: 40px;
}
form label, form legend{
    display: block;
    font-size: 20px;
    margin: 0 0 10px;
}  
.input-padron {
    display: block;
    margin: 0 0 20px;
    padding: 10px 25px;
    width: 50%;
}
.checkbox {
    margin: 20px 0;
}