Preventing “double” borders in CSS

Question

Say I have two divs next to each other (take https://chrome.google.com/webstore/category/home as reference) with a border.

Is there a way (preferably a CSS trick) to

Answer 1

I'm late to the show but try using the outline property, like so:

.item {
  outline: 1px solid black;
}

Outlines in CSS do not occupy physical space and will therefore overlap to prevent a double border.