Why are nth-of-type/nth-child selectors invalid on nested elements?

Question

I'm trying to change the style of an odd number of divs contained within one div. But the style selector nth-of-type(odd) for odd-numbered divs will affect all divs when included in another div. Here is my code for a normal div and an odd number of divs:

.video-entry-summary {
  width: 214px;
  height: 210px;
  margin-left: 10px;
  float: left;
  position: relative;
  overflow: hidden;
  border: 1px solid black;
}

.video-entry-summary:nth-of-type(odd) {
  width: 214px;
  height: 210px;
  margin-left: 0px;
  float: left;
  position: relative;
  overflow: hidden;
  border: 1px solid black;
  background: #ccc;
}

<div id="post-501" class="post-501 post type-post status-publish format-standard hentry category-moto-dz- films tag-news-sub-2">
  <div class="video-entry-summary">
    video 1
  </div>
</div>

<div id="post-240" class="post-240 post type-post status-publish format-standard hentry category-videos">
  <div class="video-entry-summary">
    video 2
  </div>
</div>

<div id="post-232" class="post-232 post type-post status-publish format-standard hentry category-videos">
  <div class="video-entry-summary">
    video 3
  </div>
</div>

<div id="post-223" class="post-223 post type-post status-publish format-standard hentry category-videos">
  <div class="video-entry-summary">
    video 4
  </div>
</div>

For some reason, the nth-of-type selectors don't work when included in my div, but they work when they are not included in any div.

Working version when not enclosed in a div:

.video-entry-summary {
  width: 214px;
  height: 210px;
  margin-left: 10px;
  float: left;
  position: relative;
  overflow: hidden;
  border: 1px solid black;
}

.video-entry-summary:nth-of-type(odd) {
  width: 214px;
  height: 210px;
  margin-left: 0px;
  float: left;
  position: relative;
  overflow: hidden;
  border: 1px solid black;
  background: #ccc;
}

<div class="video-entry-summary">
  video 1
</div>

<div class="video-entry-summary">
  video 2
</div>

<div class="video-entry-summary">
  video 3
</div>

<div class="video-entry-summary">
  video 4
</div>

How can I make the initial code the same as above?

Answer 1

:nth-of-type() is similar to :nth-child(), they must come from the same parent element. If you need these wrapped div, you should use :nth-of-type():

on these wrappers

div.post:nth-of-type(odd) .video-entry-summary {
    width:214px; 
    height:210px; 
    margin-left:0px;
    float:left;
    position:relative; 
    overflow:hidden; 
    border:1px solid black; 
    background:#ccc; 
}

If all sibling elements are .post, you should use :nth-child() to avoid conflicts with : The true meaning of nth-of-type()Confusion:

.post:nth-child(odd) .video-entry-summary {
    width:214px; 
    height:210px; 
    margin-left:0px;
    float:left;
    position:relative; 
    overflow:hidden; 
    border:1px solid black; 
    background:#ccc; 
}

.video-entry-summary {
  width: 214px;
  height: 210px;
  margin-left: 10px;
  float: left;
  position: relative;
  overflow: hidden;
  border: 1px solid black;
}

.post:nth-child(odd) .video-entry-summary {
  width: 214px;
  height: 210px;
  margin-left: 0px;
  float: left;
  position: relative;
  overflow: hidden;
  border: 1px solid black;
  background: #ccc;
}

<div id="post-501" class="post-501 post type-post status-publish format-standard hentry category-moto-dz-films tag-news-sub-2">
  <div class="video-entry-summary">
    video 1
  </div>
</div>

<div id="post-240" class="post-240 post type-post status-publish format-standard hentry category-videos">
  <div class="video-entry-summary">
    video 2
  </div>
</div>

<div id="post-232" class="post-232 post type-post status-publish format-standard hentry category-videos">
  <div class="video-entry-summary">
    video 3
  </div>
</div>

<div id="post-223" class="post-223 post type-post status-publish format-standard hentry category-videos">
  <div class="video-entry-summary">
    video 4
  </div>
</div>