Grid Classes Not Exist in CSS Files but Appears in Maps

[HadyShaltout]

I'm trying to use the new grid css but I noticed that it's not available by default in CSS files but after searching for a class [.g-col] for example it's available in map files .g-col#{$infix}-#{$i} but not in CSS, So how to use grid or generate it?

<div class="grid text-center">
    <div class="g-col-4">.g-col-4</div>
    <div class="g-col-4">.g-col-4</div>
    <div class="g-col-4">.g-col-4</div>
</div>