.div_main {
  position: absolute; 
  width: 500px; 
  left: 50%; 
  margin-left: -250px; 
  height: 350px; 
  top: 25%;
  background-image: url(images/login.jpg);
}
@media ( max-width: 520px ) {
  .div_main {
    margin-left: 0; left:0
  }
}

.div_login {
  border: solid 1px #555; 
  width: 312px; 
  margin: 108px 0 0 128px; 
  padding: 12px;
}

.label {
  width: 80px; 
  padding-top: 2px;
}

.edit {
  width: 165px;
}