Slanting Corners

Ok, so I want to get rid of the boxy look of this site Ive created. I don’t want to stray too far, so I had an idea to make some slanted lines which I think would fit nicely with the menu. How can I get the right hand blue column to have a top left slanted border and a bottom left slanted border? I understand I have to use images, but how exactly would the positioning work to be cross browser compatible?

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