so müsste es gehen
.login {
max-width: 100%;
top: 100px;
left: 50%;
top:0px;
width: 600px;
height: 0px;
margin: 10px;
float: right;
}
.slider {
top: 100px;
left: 0%;
max-width: 50%;
width: 750px;
height: 600px;
background: url('../../images/slider2.jpg');
background-size: contain;
background-repeat: no-repeat;
}