.Body {
background-color:[var,colors.main]
}

.BurgerBar {
background-color:[var,colors.black]
}

.BurgerBar {
background-color:[var,colors.black]
}
.Burger:hover {
background-color: [var,colors.black];
}
.Burger:hover .BurgerBar {
background-color: [var,colors.white];
}

[var,colors.black] & [var,colors.white] must be defined in content/system/variables

If your system/classes item gets too large & busy, split it into groups of classes using [include]:

[include,system/classes-header]
[include,system/classes-body]
[include,system/classes-footer]

Create a folder to hold them:

[include,system-classes/header]
[include,system-classes/body]
[include,system-classes/footer]