GRRR Block mixin with CSS Grid

At GRRR we have a block mixin that ensures an element has a max-width and will always be in the center of the screen. Sometimes, you want something to grow on the "overflow" on the left and right size of the container. So if the page is 1200px and the container is max 600px wide, one element is 600px wide and the other is 300px wide. See image.