how to get 3:4 container aspect ratio dynamic sized to screen size on flexible container??

can somebody help me how i do this?

i'm getting mad trying to figure this out.

Why cannot i just get height = width/3*4 ???

i think about base on screen height and also base width on height /4 * 3 . but this doesn't work properly on dynamic screen sizes to get nice looking theme.

any suggestions are welcome!

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