In this lesson we will take a look at the simplest selectors that are available, which you will probably use the most in your work.
| Prerequisites: | Basic computer literacy, basic software installed, basic knowledge of working with files, HTML basics (study Introduction to HTML), and an idea of how CSS works (study CSS first steps.) |
|---|---|
| Objective: | To learn about the different CSS selectors we can use to apply CSS to a document. |
Type selectors
A type selector is sometimes referred to as a tag name selector or element selector, because it selects an HTML tag/element in your document. In the example below we have used the span, em and strong selectors. All instances of <span>, <em> and <strong> elements are therefore styled accordingly.
Try adding a CSS rule to select the <h1> element and change its color to blue.
The universal selector
The universal selector is indicated by an asterisk (*) and selects everything in the document (or inside the parent element if it is being chained together with another element and a descendant combinator). In the following example we have used the universal selector to remove the margins on all elements. This means that instead of the default styling added by the browser, which spaces out headings and paragraphs with margins, everything is close together and we can't see the different paragraphs easily.
This kind of behavior can sometimes be seen in "reset stylesheets", which strips out all of the browser styling. Since the universal selector makes global changes, we use it to deal with very specific situations such as the one outlined below.
Using the universal selector to make your selectors easier to read
One use of the universal selector is to make selectors easier to read and more obvious in terms of what they are doing. For example, if I wanted to select the first child of any descendant element of <article> , no matter what element it was, and make it bold, I could use the :first-child selector, which we will learn more about in the lesson on pseudo-classes and pseudo-elements, as a descendant selector along with the <article> element selector:
article :first-child {
}
This could be confused however with article:first-child, which will select any <article> element that is the first child of another element.
To avoid this confusion we can add the universal selector to the :first-child selector, so it is obvious what the selector is doing. It is selecting any element which is the first-child of any descendant element of <article>:
article *:first-child {
}
Although both do the same thing, the readability is significantly improved.
Class selectors
The class selector starts with a full stop (.) character and will select everything in the document with that class applied to it. In the live example below we have created a class called .highlight, and have applied it to several places in my document. All of the elements that have the class applied are highlighted.
Targeting classes on particular elements
You can create a selector that will target specific elements with the class applied. In this next example we will highlight a <span> with a class of highlight differently to an <h1> heading with a class of highlight. We do this by using the type selector for the element I want to target, with the class appended using a dot, with no white space in between.
This approach reduces the scope of a rule as the rule will only apply to that particular element & class combination; so you would need to add another selector if you decided the rule should apply to other elements too.
Target an element if it has more than one class applied
You can apply multiple classes to an element and target them individually, or only select the element when all of the classes in the selector are present. This can be helpful when building up components that can be combined in different ways on your site.
In the example below we have a <div> that contains a note. The grey border is applied when the box has a class of notebox. If it also has a class of warning or danger, we change the border-color.
We can tell the browser that we only want to match the element if it has two classes applied by chaining them together with no white space between them. You'll see that the last <div> doesn't get any styling applied, as it only has the danger class; it needs notebox as well to get anything applied.
ID Selectors
An ID selector begins with a # rather than a full stop character, but is basically used in the same way as a class selector. An ID however can be used only once per document, and elements can only have a single id value applied to them. It can select an element that has the id set on it, and you can precede the ID with a type selector to only target the element if both the element and ID match. You can see both of these uses in the following example:
Warning: Using the same ID multiple times in a document may appear to work for styling purposes, but don't do this. It results in invalid code, and will cause strange behavior in many places.
Note: As we learned in the lesson on specificity, an ID has high specificity and will overrule most other selectors. This can make them difficult to deal with. In most cases it is preferable to add a class to the element rather than use an ID, however if using the ID is the only way to target the element — perhaps because you do not have access to the markup and so cannot edit it — this will work.
In the next article
We'll continue exploring selectors by looking at attribute selectors.