Introduction

By now you should be comfortable with basic CSS selectors and have no trouble grabbing things by their type, class or ID. But to be a real CSS surgeon, sometimes you need more specialized tools. In this lesson we’ll look at advanced CSS selectors and show you how to target elements in a more specific and finely grained way.

These selectors can be especially useful when you can’t (or don’t want to) change your HTML markup.

There are a lot of advanced selectors, so going through every single one is outside the scope of this lesson. However, we’ll go through some of the most useful and common ones, as well as arm you with the concepts and vocabulary to learn more on your own.

As always feel free to open up your code editor and run your own experiments with these selectors - practice makes perfect!

Learning Outcomes

  • Understand how to use parent and sibling selectors
  • Recognize the difference between pseudo classes and pseudo elements
  • Learn about some of the most useful and common pseudo elements and pseudo classes
  • Learn about the different ways to select an attribute or its parts

Parent and Sibling Combinators

Let’s have a look at some more ways we can access different elements without referring to their classes. Here are three new selectors to do just that.

  • > - the child combinator
  • + - the adjacent sibling combinator
  • ~ - the general sibling combinator

We’ll tackle some practical examples using this sample markup.

<main class="parent">
  <div class="child group1">
    <div class="grand-child group1"></div>
  </div>
  <div class="child group2">
    <div class="grand-child group2"></div>
  </div>
  <div class="child group3">
    <div class="grand-child group3"></div>
  </div>
</main>

By now, you should be pretty comfortable writing rules using the descendant combinator you learned about in foundations. For instance, if we wanted to select all the child and grand-child divs inside of main, we could write:

main div {
  /* Our cool CSS */
}

But what if we wanted to be more specific and select only the child or grand-child divs? That’s where the child combinator > comes in handy. Unlike the descendant combinator, it will only select direct children.

/* This rule will only select divs with a class of child */
main > div {
  /* Our cool CSS */
}

/* This rule will only select divs with a class of grand-child */
main > div > div {
  /* More cool CSS */
}

Phrased another way, the child selector will select an element that is one level of indentation down. In order to select an element that is adjacent to our target, or on the same level of indentation, we can use the adjacent sibling combinator +.

/* This rule will only select the div with the class child group2 */
.group1 + div {
  /* Our cool CSS */
}

/* This rule will only select the div with the class child group3 */
.group1 + div + div {
  /* More cool CSS */
}

Finally, if we want to select all of an element’s siblings and not just the first one, we can use the general sibling combinator ~.

/* This rule will select all of .group1's siblings - in this case the 2nd and 3rd .child divs */
.group1 ~ div {
  /* Our cool CSS */
}

Just like the descendant combinator, these selectors don’t have any special specificity rules - their specificity score will just be made up of their component parts.

Pseudo-selectors

Before diving into pseudo-selectors, a quick note on the difference between pseudo-elements and pseudo-classes. Pseudo-class selectors are prefixed with a single colon and are a different way to target elements that already exist in HTML. Pseudo-elements are prefixed with two colons and are used to target elements that don’t normally exist in the markup. If that doesn’t make sense straight away, don’t worry - we’ll explore some examples below.

Pseudo-classes

Pseudo-classes offer us different ways to target elements in our HTML. There are quite a lot of them, and they come in a couple of different flavors. Some are based on their position or structure within the HTML. Others are based on the state of a particular element, or how the user is currently interacting with it. There are too many to cover in detail here but we’ll have a look at some of the most useful ones. Pseudo-classes share the same specificity as regular classes (0, 0, 1, 0). Just like regular classes, most can be chained together.

Note: The (0,0,1,0) above is the notation for calculating specificity. To find out more about how it works, glance over the “Calculating CSS Specificity Value” section from this article on CSS Specificity

As always don’t forget to check the docs to see a complete picture of what’s available.

Dynamic and User Action Pseudo-classes

These types of useful pseudo-classes can make your page feel much more dynamic and interactive.

:focus applies to an element that is currently selected by the user either through selecting it with their cursor or using their keyboard.

:hover will affect anything under the users mouse pointer. It can be used to give extra oomph to buttons and links to highlight that they’re interactable, or to trigger a drop down menu.

:active applies to elements that are currently being clicked, and is especially useful for giving your user feedback that their action had an effect. This is a great one to give your buttons and other interactive elements more ‘tactile’ feedback.

Have you ever wondered why links are blue but turn purple when clicked in unstyled HTML? It’s because browsers implement that styling by default. To implement your own custom styling for links, take advantage of the :link and :visited pseudo-classes. A simplified version of default browser styling might look something like this:

  /* This rule will apply to all links */
  a {
    text-decoration: underline;
  }

  /* This will apply to unvisited links */
  a:link {
    color: blue;
  }

  /* And you guessed it, this applies to all links the user has clicked on */
  a:visited {
    color: purple;
  }

Structural Pseudo-classes

Structural pseudo-classes are a powerful way to select elements based on their position within the DOM.

:root is a special class that represents the very top level of your document - the one element that has no parents. Generally when working with the web, this is equivalent to the html element, but there are a few subtle differences.

:root is generally the place where you will place your ‘global’ CSS rules that you want available everywhere - such as your custom properties and CSS variables, or rules such as box-sizing: border-box;.

:first-child and :last-child will match elements that are the first or last sibling.

Similarly :empty will match elements that have no children at all, and :only-child will match elements that don’t have any siblings.

For a more dynamic approach we can use :nth-child. This is a flexible pseudo-class with a few different uses.

  .myList:nth-child(5) {/* Selects the 5th child of myList */}

  .myList:nth-child(3n) { /* Selects every 3rd child of myList */}

  .myList:nth-child(3n + 3) { /* Selects every 3rd child of myList, beginning with the 3rd */}

  .myList:nth-child(even) {/* Selects every even child of myList */}

Pseudo-elements

While pseudo-classes give us an alternative way to interact with our HTML elements based on their state or structure, pseudo-elements are more abstract. They allow us to affect parts of our HTML that aren’t elements at all. These special elements share the same specificity as regular elements (0, 0, 0, 1). There are a number of useful pseudo-elements that can be utilized in any number of creative ways.

::marker allows you to customize the styling of your <li> elements’ bullets or numbers.

::first-letter and ::first-line allow you to (you guessed it!) give special styling to the first letter or line of some text.

::before and ::after allow us to add extra elements onto the page with CSS, instead of HTML. Using it to decorate text in various ways is one common use case.

<style>
  .emojify::before {
    content: '😎 🥸 🤓';
}

  .emojify::after {
    content: '🤓 🥸 😎';
}
</style>

<body>
  <div> Let's <span class="emojify">emojify</span>this span!</div>
</body>

Using these pseudo-elements this way would give us this result:

Let’s 😎 🥸 🤓 emojify 🤓 🥸 😎 this span!

::selection allows you to change the highlighting when a user selects text on the page.

There are lots more! Have a quick browse through the pseudo-element docs to see a complete list of what’s possible.

Attribute Selectors

The last tool we’re going to add to the box is attribute selectors. Recall that an attribute is simply anything in the opening tag of an HTML element - such as src='picture.jpg' or href="www.theodinproject.com".

Since we write our own values for attributes, we need a slightly more flexible system to be able to target specific values.

Attribute selectors have the same specificity as classes and pseudo-classes (0, 0, 1, 0).

Let’s look at some examples for basic usage.

  • [attribute] - This general selector will select anything where the given attribute exists. Its value doesn’t matter.
  • selector[attribute] - Optionally we can combine our attribute selectors with other types of selectors, such as class or element selectors.
  • [attribute="value"] - To get really specific, we can use = to match a specific attribute with a specific value.
  [src] {
    /* This will target any element that has a src attribute. */
  }

  img[src] {
    /* This will only target img elements that have a src attribute. */
  }

  img[src="puppy.jpg"] {
    /* This will target img elements with a src attribute that is exactly "puppy.jpg" */
  }

Sometimes we need to be more general in how we access these attributes. For example, perhaps we’re only interested in img elements where the src attribute’s value ends in .jpg. For cases like this we have some attribute selectors that allow us to match a part of the attribute’s value. If you’ve ever come across regular expressions before, these attributes use a similar syntax.

  • [attribute^="value"] - ^= Will match strings from the start.
  • [attribute$="value"] - $= Will match strings from the end.
  • [attribute*="value"] - *= The wildcard selector will match anywhere inside the string.
[class^='aus'] {
  /* Classes are attributes too!
    This will target any class that begins with 'aus':
    class='austria'
    class='australia'
  */
}

[src$='.jpg'] {
  /* This will target any src attribute that ends in '.jpg':
  src='puppy.jpg'
  src='kitten.jpg'
  */
}

[for*='ill'] {
  /* This will target any for attribute that has 'ill' anywhere inside it:
  for="bill"
  for="jill"
  for="silly"
  for="ill"
  */
}

To see what other things you can achieve with attribute selectors, such as searching case insensitivity, or sub-strings separated by hyphens, have a browse through the MDN docs.

Assignment

  1. Complete CSS Diner. You should be familiar with most of the content in the first couple of exercises, but practice and review never hurt! Don’t forget to read the examples and explanations on the right.
  2. Read Shay Howe’s article on Complex Selectors. This covers most of the content of this lesson in a bit more detail.

Additional Resources

This section contains helpful links to other content. It isn’t required, so consider it supplemental for if you need to dive deeper into something.

Knowledge Check

This section contains questions for you to check your understanding of this lesson. If you’re having trouble answering the questions below on your own, review the material above to find the answer.

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