CSS selectors are patterns that match elements in a document. Use them in stylesheets to target elements for styling, or pass them to JavaScript’s querySelector() and querySelectorAll() methods to find elements in the DOM.
Choose a selector that describes what you need
Begin with an element’s type, class, ID, or attributes. Add more conditions or relationships only when they help distinguish the target.
| What to match | Selector form | Example |
|---|---|---|
| Elements of a particular type | Type selector | button |
| Any element | Universal selector | * |
| An element with a class | Class selector | .notice |
| An element with an ID | ID selector | #main |
| An element with an attribute or attribute value | Attribute selector | input[type="email"] |
| One element meeting several conditions | Compound selector | button.primary[disabled] |
| A state or structural condition | Pseudo-class | input:focus, li:first-child |
| A stylable part of an element | Pseudo-element | p::first-line |
| Elements matching any of several selectors | Selector list | h1, h2 |
These selector forms are described in the W3C Selectors Level 4 specification and MDN’s CSS selectors reference.
Combine selectors to express relationships
Conditions written together without a combinator apply to the same element: button.primary[disabled] matches a button that has the primary class and the disabled attribute. A combinator connects different parts of the document structure.
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| Relationship | Combinator | Example | Meaning |
|---|---|---|---|
| Descendant | Whitespace | article p |
A paragraph anywhere inside an article |
| Direct child | > |
ul > li |
A list item whose parent is a list |
| Immediately following sibling | + |
h2 + p |
A paragraph immediately after a heading, with the same parent |
| Later sibling | ~ |
h2 ~ p |
A paragraph later than a heading, with the same parent |
A comma means “match either selector,” not “match both conditions on one element.” For example, h1, h2 selects headings of either type. A compound selector such as h1.title instead requires one element to satisfy both conditions.
Use selectors in JavaScript to retrieve elements
Use querySelector() when you need the first matching element, and querySelectorAll() when you need all matches. An element-scoped query searches that element’s descendants.
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const firstButton = document.querySelector("button.primary");
const allButtons = document.querySelectorAll("button");
const panel = document.querySelector("#panel");
const nestedLink = panel?.querySelector("a[href]");querySelector() returns the first matching Element, or null if there is no match. querySelectorAll() returns the matching elements as a collection. The optional chaining in the example prevents an error if no panel is found; without it, calling querySelector() on null would fail. See MDN’s Document.querySelector() reference and MDN’s Element.querySelector() reference.
Escape dynamic IDs and class names
HTML permits ID and class values that are not valid CSS identifiers. If a value comes from data and may contain punctuation or other special characters, escape it before inserting it into a selector. Keep the selector structure fixed rather than concatenating arbitrary untrusted text as selector syntax.
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const id = "item:42";
const element = document.querySelector(`#${CSS.escape(id)}`);If a selector string is invalid, the query method throws a SyntaxError rather than returning null. Refer to the MDN CSS.escape() reference when building selectors from dynamic values.
Know what selectors do—and do not—return
- Pseudo-class versus pseudo-element: A pseudo-class adds a matching condition, often based on state or structure. A pseudo-element describes a stylable part. Use the modern double-colon form, as in
::first-line; a few legacy pseudo-elements also support single-colon notation for compatibility. - Pseudo-elements are not DOM elements: A stylesheet can target
p::first-line, butquerySelector()does not return a pseudo-element as anElement. - Duplicate IDs: IDs should be unique in well-formed markup. If duplicates exist, a first-match query for that ID returns only the first match in document order.
- Stylesheet specificity: If cascade conflicts matter, note that
:is()takes the specificity of its most specific argument, while:where()contributes zero specificity. Consult the W3C specification for the relevant selector rules.
Check support for newer selector features
The W3C document identifies Selectors Level 4 as a Working Draft dated 22 January 2026; a specification describes syntax, not guaranteed support in every browser, automation tool, or embedded environment. MDN describes querySelector() as widely available across browsers since July 2015, but that does not establish support for every newer selector feature. Check compatibility for the specific selector and target environments your project uses.
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Frequently Asked Questions
Can a CSS selector match more than one element?
Yes. A selector can match multiple elements; use JavaScript’s querySelectorAll() when you need all of them.
Does querySelector() return an empty result when no element matches?
No. It returns null when there is no match. An invalid selector instead throws a SyntaxError.
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