Selector Grouping

Use the comma (,) separator to group selectors. The following declaration block will be applied to any element that matches any selector in the group:

<code class="language-css">td, th {
  /* 声明 */
}</code>

We can treat commas as logical "OR" operators, but we must remember that each selector in the group is independent. A common beginner mistake is to write groups like this:

<code class="language-css">#foo td, th {
  /* 声明 */
}</code>

Beginners may think that the above declaration block will be applied to all descendants of the td and th elements of the element with ID "foo". However, the above selector group is actually equivalent to:

<code class="language-css">#foo td {
  /* 声明 */
}
th {
  /* 声明 */
}</code>

To achieve your true goal, write the selector group as follows:

<code class="language-css">#foo td, #foo th {
  /* 声明 */
}</code>

Important Tips: No need to trail commas Do not leave commas after the last selector in the group!

FAQs on CSS selector grouping

What is the purpose of CSS selector grouping?

CSS Selector Grouping is a CSS technology that applies the same style rules to multiple selectors. Instead of writing the same rules for different selectors multiple times, you can put them together and write the rules only once. This not only makes your CSS code more concise and easy to read, but also reduces the size of your CSS file, which can reduce the load time of your website.

How to group selectors in CSS?

To group selectors in CSS, simply list the selectors to be grouped together, separated by commas, and then the declaration block. For example, if you want to apply the same style to h1, h2 and p elements, you should write it as follows:

<code class="language-css">h1, h2, p {
  color: blue;
}</code>

This applies blue to all h1, h2 and p elements.

Can different types of selectors be combined together?

Yes, you can combine any type of selector together, including element selectors, class selectors, ID selectors, and more. For example, you can combine element selectors with class selectors as follows:

<code class="language-css">h1, .intro {
  color: blue;
}</code>

This applies blue to all h1 elements and any element with class "intro".

What happens if a selector in a group has a different style rule?

If one selector in a group has a different style rule, a single rule will override the group rule. This is because in CSS, the last defined rules take precedence. For example, if you have the following code:

<code class="language-css">h1, h2, p {
  color: blue;
}

p {
  color: red;
}</code>

The

p element will be red, not blue, because the individual rule of p is behind the group rule.

Can selectors nested in other elements be grouped?

Yes, you can group selectors nested in other elements. This is often used to apply styles to specific parts of a web page. For example, you can group selectors to style all div and h1 elements in the p element, as shown below:

<code class="language-css">td, th {
  /* 声明 */
}</code>

This applies blue to all div and h1 elements within the p element.

Can pseudo-classes and pseudo-elements be used in a selector group?

Yes, you can use pseudo-classes and pseudo-elements in the selector group. For example, you can group selectors to set the hover state of the link and the style of the before pseudo-element of the paragraph as follows:

<code class="language-css">#foo td, th {
  /* 声明 */
}</code>

This applies blue to the hover state of all links and the before pseudo-element of all paragraphs.

What is the difference between selector grouping and selector chaining?

Selector grouping and selector chaining are two different techniques in CSS. When you group selectors, you apply the same style rules to multiple selectors. When you link selectors, you apply style rules to elements that match all link selectors. For example, h1, h2 is a selector group, and h1.h2 is a link selector.

Can selectors be grouped into media queries?

Yes, you can group selectors into media queries. This is useful for applying different styles to different screen sizes. For example, you can group selectors to change the colors of the h1 and p elements on the small screen, as shown below:

<code class="language-css">#foo td {
  /* 声明 */
}
th {
  /* 声明 */
}</code>

When the screen size is 600px or smaller, this applies blue to all h1 and p elements.

How to debug the problem of group selector?

The problem of group selector can be debugged using the browser's developer tools. You can check elements to see which styles are being applied and which selectors are coming from. If the style is not applied as expected, check the typo in the selector to ensure correct specificity, and make sure the style is not overwritten by other rules.

What are the limitations or disadvantages of using group selectors?

While group selectors can make your CSS more concise and manageable, they can also make your CSS harder to read if overused. Too many selectors in a group can make it difficult to understand what elements the style is applied to. It must also be remembered that all selectors in the group will share the same specificity, which may affect how the style is applied if you have other conflicting rules.

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