Minor fixes

[therealcoder1337]

1. For the Layout with view="lHh Lpr lFf", the right part of the QHeader becomes hidden once the drawer is opened. It can be fixed with a SCSS like:

.q-drawer--active ~ .q-header {
    $drawer-width: 300px;
    width: calc(100% - $drawer-width);
}

2. We should change the body class indicating light or dark mode to body--light and body--dark, respectively.

[KilDesu]

1. Fixed in #37
2. Fixed in #36