I’m using Bueno theme, and I’ve got it set so that a 3px black border appears around images in my posts. I set the max width for images to 864, but when I post images at 864 px wide now the black border doesn’t appear around the right side of the image though it does appear around the other 3 sides. I have tried changing the max width to 867 to account for the 3 px border, and also tried changing the display width of images to 861 when I insert media but neither of those have fixed the problem.
I tried changing the display width of images to 861 when I insert media.
If the max-width for images is set to 861px and you add a 3px border, then the final width for that element should be 867px. You adjust it by 6px because 3px is taken up on both the left and right side.
However, I just checked your blog and I see that the current width for posts is 840px, you have added the following custom CSS to give a 5px black border (which takes up 10px total, and you’ve set images inside posts to have a max-width of 830px.