Overriding BootStrap CSS - difficulty understanding specificity - html

Question

I'm absolutely new to coding and attempting a basic website, and have used the BootStrap CSS as a basis.
I've set up nav-pills and managed to customise them thus far (spacing, font, background colours etc) but struggled for hours trying to change the background colour of my header behind the nav-pills - 1 white b/g to 2 grey b/g.
My HTML header container reads:
<div class="header">
<div class="row">
<p id="navigator">
[nav-pills code]
</>
</div>
</div>
With a lot of researching into specificity I thought this may be my problem so I tried CSS code:
.header .row #navigator {
background-color: #CCCDD9;
}
to no avail, but found that simply did work:
.header .row {
background-color: #CCCDD9;
}
now produced the desired override of the bootstrap CSS even though I was not even selecting the #navigator ID to increase rule specifity. Could someone explain why this method works?
Further, as the new background does not appear for the other website pages I did not add the #navigator header ID to, is there a method (besides adding the #navigator ID to each HTML page) of modifying my CSS which would make this override work across all pages?

Answer 1

In your first CSS example, you are targeting the paragraph tag within the row, but in the HTML you provided your paragraph tag is malformed (missing a closure and contains no content). Because of this, the paragraph tag is being rendered with 0 height which explains why you don't see the background color. If you add content to the paragraph tag and you add a closure, it will work with the first bit of CSS you posted.
In other words, this is not a specificity issue.
<div class="header">
<div class="row">
<div class="col-sm-12">
<p id="navigator">Testing</p>
</div>
</div>
</div>
Bootply Example
After re-reading your question, I don't think you should be using a paragraph tag at all. It looks like you were trying to use it as a container for the pills, but you should be using either an unordered list (like in the Bootstrap docs example or a div). Here's some sample code:
HTML:
<div class="header">
<div class="row">
<div class="col-sm-12">
<ul class="nav nav-pills">
<li role="presentation" class="active">Home</li>
<li role="presentation">Profile</li>
<li role="presentation">Messages</li>
</ul>
</div>
</div>
</div>
CSS:
.nav-pills {
background-color: #CCCDD9;
}
Bootply