Custom Properties

<style>
:root{
    --green: #6aaa64;
    --darkYellow: #b59f3b;
}
div.green{
    background:var(--green);
    padding:1rem 2.5rem;
    margin:1rem;
    width:10%;
}
div.yellow{
    background:var(--darkYellow);
    padding:1rem 2.5rem;
    margin:1rem;
    width:10%;
}
</style>