I created some bins with windows that you can slide in from the top. As a window i use the dividers that you can find in those flimsy plastic boxes that some of my parts come in. Because i wanted to sort the content of those plastic boxes in gridfinity bins i decided to recycle the plastic dividers to be used as windows. the dividers are not clear plastic so you can't see clearly trough them but its good enough to generally know whats inside or to see if the bin is empty or not when its stacked ( and viewable from the front). Once i have sorted all the boxes i'm gonna try to cut the plastic boxes to make bigger windows with clear plastic.

window hole size: 28.5 x 18.5 mm
window sliding slot size: 31 x 0.5 slot at the bottom and to gridfinity at the top.

thickness is 1.1mm. so its a tight tolerance to push the window in from the top.