How to select a range of elements in repeated pattern

Question

Let's say there are 12 items in 4 rows.

 |  1   ||  2   ||  3   |
 |  4   ||  5   ||  6   |
 |  7   ||  8   ||  9   |
 |  10  ||  11  ||  12  |

I want to select and style 2nd row and 4th row, How do I do that?

Note that rows are not in different HTML elements, in fact they are all an ul li element.

Desired Result:

 |  1   ||  2   ||  3   |
 |--4---||--5---||--6---|
 |  7   ||  8   ||  9   |
 |--10--||--11--||--12--|

I have tried playing with this:

li:nth-child(n+4)

It selects all the elements after first three. Then I tried this:

li:nth-child(n+4):nth-child(-n+8)

This only selects 4, 5 & 6 but I cant repeat this pattern to select 10, 11 & 12 as well. Is there any solution for this in CSS?

Answer 1

This is a commonly-asked question, but I wanted to point out that the reason :nth-child(n+4):nth-child(-n+6) only matches one specific range of elements is that it only provides a single start point (n+4) and a single end point (-n+6). The only elements that can be greater than or equal to 4 and less than or equal to 6 are 4, 5 and 6, so it's impossible to match elements outside of this range using the same selector. Adding more :nth-child() pseudos will only narrow down the matches.

The solution is to think of this in terms of columns, assuming there will always be exactly 3 columns (elements) per row. You have three columns, so you will need three separate :nth-child() pseudos. Elements 4 and 10 from the first column are 6 elements apart, so the argument to all of the :nth-child() pseudos needs to start with 6n.

The +b portion in the An+B expression can either be +4, +5 and +6, or 0, -1 and -2 — they will both match the same set of elements:

• li:nth-child(6n+4), li:nth-child(6n+5), li:nth-child(6n+6)
• li:nth-child(6n), li:nth-child(6n-1), li:nth-child(6n-2)

You cannot do this with a single :nth-child() pseudo-class, or a single compound selector consisting of any combination of :nth-child() pseudos, because the An+B notation simply doesn't allow such expressions to be constructed that match elements in ranges as described.