body {
    background-color: lightgrey;
    height:100vh;
    width:100vw;
    margin: 0 !important;
    padding: 0 !important;
}
.mainPanel {
    margin: auto;
    width: 80%;
    height: 100vh;
    background-color: white;
}
@media (orientation: landscape) {
    .mainPanel {
        width: 60%;
    }
}