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Structural CSS Selectors

June 05, 2021


Yeah, you read that right. Let go straight into it!

A Test Case

Can you interprete this CSS selector query?

p.title:first-of-type {
color: red;
}

Let me think like you would:

Select every P element that has the class name of title and apply the color red to the first of its type.

<body>
<p>Lorem Ipsum</p>
<p class="title">Paragraph 2 (shows in red color)</p>
</body>

You think you’re right.

Another test case

What happens with the below:

<style>
p.paragraph-1:first-child {
color: green;
}
</style>
<div>
<p class="paragraph-1">
<span class="span1">This is the title</span>
<span class="span2"> Shouldn't be the title </span>
</p>
</div>

You would expect the SPAN with the class name span1 should have the color green.

To you, the query reads:

Select the first child of every P tag that has a class name of paragraph-1,

Well,that is not correct!

The query correctly reads:

Select every P tag with a class name of paragraph-1 and IT IS THE FIRST CHILD of its parent.

Know the Strcuture

To better understand Structural selectors in CSS, we have to consider the query first and then attach the selector’s semantic meaning.

:only-child should read as AND IS THE ONLY CHILD, but not seeing it as going deeper to the actual element’s children.

Structural selectors always refer to the position of an element itself in a document.

<p>
<h1>1</h1>
<h1>2</h1>
</p>

For the structure above, h1:first-child would pick the first h1, h1:last-child would select the second h1.

The beauty of structural selectors is that page structures are stylable regardless of their complexity.

For example, the only child of an element, empty elements, any element that is a child to an element but existing at an index, and more are stylable, which is powerful!

Ref List

Reference the list below to understand structural selectors proper:

  • <selector>:first-child - Will match any element that is the first child
  • <selector>:last-child - will match any element that is the last child
  • <selector>:only-child - will match any element that is the only child of its element
  • <selector>:nth-child(n) - will match any element that is a child of a parent element but occurring at the index of n for that selector
  • <selector>:nth-last-child(n) - will match any element that is a child element occurring at the index of n for that selector. Take it as `nth-child moving in reverse mode.
  • <selector>:empty - will match any element that is empty or has just comments
  • <selector>:first-of-type - will match any element, and it is the first occurrence for that selector
  • <selector>:last-of-type - will match any element that is the last occurrence for that selector
  • <selector>:nth-of-type(n) - will match any element occurring at index of n for that selector
  • <selector>:nth-last-of-type(n) - will match the last element for every element occurring at the index of n for that selector. Take it as nth-type moving in reverse mode.
  • <selector>:only-of-type - will match the only element that has for that selector.

Interesting right? Play with it here.

Take home: Structural selectors apply themselves to the selected element to help us style an element existing at a specific position in the HTML.

au revoir!

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With 💗 by Aleem Isiaka.
Software Engineer >>> Computer && Machines | Learner && Writer