can anyone help me to find a CSS solution here, please?
here is a scribble:

The wrapper has a variable width and the inside space of the floating boxes should exactly 1px. the margin-bottom is no problem – but the margin on the left/right side. how to solve this with width:33%?? 🙁
Thanks in advance.
EDIT: this would be a mobile friendly page. so there are fewer columns if the browser size is smaller. i will do this with @media.
where
Extremely fluid design. some glitches may be visible in different resolutions, but should work in most cases.