What is the best (simplest/most efficient) way to make a css grid fill the height of the window at any size without using
To achieve what you want to do, you could use viewport units. These are based on the viewport size (the size of your browser window).
1vh = 1% of the viewport height
1vw = 1% of the viewport width
So, to scale an element as wide/high as the viewport, you could just use:
100vh / 100vw. In your case that would be