Need some explanation on HTML, nth-child

Question

NOTE: SEE BELOW FOR CLEARER EXPLANATION

I'm trying to figure out why this is happening.

jsFiddle 1 - Before

HTML

<div class="chicken">
    <div class="big-chix">Contento</div>
    <div class="big-chix">Contento</div>
    <div class="big-chix">Contento</div>
    <div class="big-chix">Contento</div>
    <div class="big-chix">Contento</div>
    <div class="big-chix">Contento</div>
</div>

CSS

.chicken { width:100%; background:#999; float:left; }

.big-chix { width:48%; margin:0.5%; padding:0.5%; background:#666; float:left; }

.big-chix:nth-child(2n+1) { background-color:#eee; }
.big-chix:nth-child(2n+2) { background-color:#aaa; }

What I'm trying to achieve here is to put a different background for .big-chix class for nth children 1, 3 , 5... and 2, 4, 6...

But when I put in a paragraph (or anything else like a div, etc for that matter), it becomes like this:

jsFiddle 2 - After

HTML

<div class="chicken">
    <p>paragraphy</p>
    <div class="big-chix">Contento</div>
    <div class="big-chix">Contento</div>
    <div class="big-chix">Contento</div>
    <div class="big-chix">Contento</div>
    <div class="big-chix">Contento</div>
    <div class="big-chix">Contento</div>
</div>

CSS

.chicken { width:100%; background:#999; float:left; }

.big-chix { width:48%; margin:0.5%; padding:0.5%; background:#666; float:left; }

.big-chix:nth-child(2n+1) { background-color:#eee; }
.big-chix:nth-child(2n+2) { background-color:#aaa; }

The nth-child placement switches places. Why is this so? Isn't .big-chix:nth-child() only suppose to select all the .big-chix classes (which is 6 .big-chix), then set 1, 3, 5 to a background-color of #eee, and 2, 4, 6 to #aaa?

---

EDIT: From what I gather, nth-child will not apply to an element child in the element parent in a code like this:

jsFiddle - nth-child(1) when <p> paragraph is the first element

HTML

<div class="chicken">
    <p>paragraphy</p> [this is nth-child(1)]
    <div class="big-chix">Contento</div> [this is nth-child(2)]
    <div class="big-chix">Contento</div> [this is nth-child(3)]
    <div class="big-chix">Contento</div> [this is nth-child(4)]
    <div class="big-chix">Contento</div> [this is nth-child(5)]
    <div class="big-chix">Contento</div> [this is nth-child(6)]
    <div class="big-chix">Contento</div> [this is nth-child(7)]
</div>

CSS

.chicken { width:100%; background:#999; float:left; }

.big-chix { width:48%; margin:0.5%; padding:0.5%; background:#666; float:left; }

.big-chix:nth-child(1) { background-color:#eee; }

BUT, it will work in a parent element that has .big-chix as the first element.

jsFiddle - nth-child with .big-chix as the first element

HTML

<div class="chicken">
    <div class="big-chix">Contento</div> [this is nth-child(1)]
    <p>paragraphy</p> [this is nth-child(2)]
    <div class="big-chix">Contento</div> [this is nth-child(3)]
    <div class="big-chix">Contento</div> [this is nth-child(4)]
    <div class="big-chix">Contento</div> [this is nth-child(5)]
    <div class="big-chix">Contento</div> [this is nth-child(6)]
    <div class="big-chix">Contento</div> [this is nth-child(7)]
</div>

CSS

.chicken { width:100%; background:#999; float:left; }

.big-chix { width:48%; margin:0.5%; padding:0.5%; background:#666; float:left; }

.big-chix:nth-child(1) { background-color:#eee; }

Answer 1

use these

.big-chix:nth-child(even) { background-color:#eee; }
.big-chix:nth-child(odd) { background-color:#aaa; }

works in http://jsfiddle.net/TeqUF/2/

Answer 2

Isn't .big-chix:nth-child() only suppose to select all the .big-chix classes (which is 6 .big-chix), then set 1, 3, 5 to a background-color of #eee, and 2, 4, 6 to #aaa?

No.

:nth-child() selects "The nth element in the parent", not "The nth element that also matches the other parts of the selector".

Each selector is applied independently and only elements that match all the components will match the complete selector.

Note, however, that there is :nth-of-type() which should do what you want.