nth-child doesn't respond to class [duplicate]

Question

Is it possible to get the nth-child pseudo-selector to work with a specific class?

See this example: http://jsfiddle.net/fZGvH/

I want to have the second DIV.red turn red, but it doesn't apply the color as expected.

Not only that, but when you specify this, it changes the 5th DIV to red:

div.red:nth-child(6)

When you specify this, it changes the 8th DIV to red:

div.red:nth-child(9)

It seems to be one DIV behind. There are only 8 DIV tags in the example so I don't know why nth-child(9) even works. Testing using Firefox 3.6, but in my actual production code the same problem occurs in Chrome. I'm not understanding something about how this is supposed to work, would appreciate clarification.

Also, this will change the 6th DIV to red, but what I actually want is for it to change the second DIV.red to red:

div.red:nth-of-type(6)

And I don't understand why nth-child() and nth-of-type() respond differently, since there are only eight tags of the same type in the document.

Answer 1

There's no way to filter by class in CSS because there's no :nth-of-class() selector. One way around this is to put your two different kinds of divs into their own groups, then select based on those groups. For example:

<div class="orange">
  <div></div>
  <div></div>
  <div></div>
  <div></div>
</div>

<div class="red">
  <div></div>
  <div></div>
  <div></div>
  <div></div>
</div>

With this selector:

div.red div:nth-child(2) {
    background: red;
}

---

Regarding the last bit of your question:

And I don't understand why nth-child() and nth-of-type() respond differently, since there are only eight tags of the same type in the document.

For the code you give there shouldn't be any difference. I tested it, and the two pseudo-classes work as expected. But, in general:

:nth-child() operates on an entire level of siblings without regard for any other simple selectors. Then if the nth child is not among what's matched by the simple selectors, nothing is matched.

:nth-of-type() operates on a level of siblings of the given type without regard for other simple selectors. Then if the nth element occurring of that type is not among what's matched by the simple selectors, nothing is matched.

Answer 2

You can use the general sibling combinator:

div,
div.red ~ div.red ~ div.red {
  background: gray;
}
div.red ~ div.red {
  background: red;
}

It is verbose and you need to reset the styles back again, but it could be useful in some special situations.

It could be automated with a CSS preprocessor, and if I understand gzip correctly, since the CSS ouput is just repeating the same text the gziped file size should not be terribly big unless you use it a lot.

Answer 3

there's a simpler solution that I have found to work with my divs without any special lines of code.

.red div:nth-child(6) {background-color:#ccc;}
.red div:nth-child(9) {background-color:#eee;}

works just fine as well without the div in front.