The following uses three nested divs (meaning, divs inside each other).
Each inside div is set to be smaller in width and height than the divs it is inside of.
To resolve the above replication challenge, check out the two working solutions:
Solution 2 - concentricCSSsquares2.html - Solved using relatively positioned divs that are inside each other
Solution 3 - concentricCSSsquares3.html - Solved with a few different sizes of divs plus some CSS padding settings