How to make border like this?

bede6f1ec25d4524b0776438ffacb0a2.png
You need to upper right corner was cut like the picture
June 27th 19 at 14:57
1 answer
June 27th 19 at 14:59
https://codepen.io/anon/pen/Zedexv perhaps perversely , but in General it is easier to picture add background:)

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