you can cover each window like this and just ignore that they are different sizes.
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blinds alone give a lighter more modern look...but your furniture looks very traditional, which I think calls for floor to ceiling drapes.
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you can do a curtain wall. open from each end OR from the middle, to reveal equal amount of each window (keeping half the big window covered). This will fill the room and make it feel too heavy if you use dark heavy fabric. But if fabric is too sheer you will see windows even when closed.....
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You could do drapes on outside of windows only like this photo and cover larger window so windows look same size. Be sure both widths of fabric are same width. I like this light fabric print similar to wall color with a different color binding.
you can cover each window like this and just ignore that they are different sizes.
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