CSS 선택자

This translation is in progress.

CSS 에서, 선택자는 스타일을 지정할 웹 페이지의 HTML 요소를 대상으로 하는 데 사용됩니다. 사용 가능한 다양한 CSS 선택자가 있으며, 스타일을 지정할 요소를 선택할 때 세밀한 정밀도를 허용합니다. 이 기사와 하위 기사에서는 다양한 유형을 자세히 살펴보고 작동 방식을 살펴 보겠습니다.

전제조건: 기본 컴퓨터 활용 능력, 기본 소프트웨어 설치파일 작업 에 대한 기본 지식, HTML 기본 사항 (HTML 소개 학습) 및 CSS 작동 방식에 대한 이해 (CSS 첫 단계 학습)
목적: CSS 선태자 작동 방식에 대해 자세히 알아보기.

What is a selector?

You have met selectors already. A CSS selector is the first part of a CSS Rule. It is a pattern of elements and other terms that tell the browser which HTML elements should be selected to have the CSS property values inside the rule applied to them. The element or elements which are selected by the selector are referred to as the subject of the selector.

Some code with the h1 highlighted.

In earlier articles you met some different selectors, and learned that there are selectors that target the document in different ways — for example by selecting an element such as h1, or a class such as .special.

In CSS, selectors are defined in the CSS Selectors specification; like any other part of CSS they need to have support in browsers for them to work. The majority of selectors that you will come across are defined in the Level 3 Selectors specification, which is a mature specification, therefore you will find excellent browser support for these selectors.

Selector lists

If you have more than one thing which uses the same CSS then the individual selectors can be combined into a selector list so that the rule is applied to all of the individual selectors. For example, if I have the same CSS for an h1 and also a class of .special, I could write this as two separate rules.

h1 { 
  color: blue; 
} 

.special { 
  color: blue; 
} 

I could also combine these into a selector list, by adding a comma between them.

h1, .special { 
  color: blue; 
} 

White space is valid before or after the comma. You may also find the selectors more readable if each is on a new line.

h1, 
.special {
  color: blue; 
} 

In the live example below try combining the two selectors which have identical declarations. The visual display should be the same after combining them.

 

When you group selectors in this way, if any selector is invalid the whole rule will be ignored.

In the following example, the invalid class selector rule will be ignored, whereas the h1 would still be styled.

h1 { 
  color: blue; 
} 

..special { 
  color: blue; 
} 

When combined however, neither the h1 nor the class will be styled as the entire rule is deemed invalid.

h1, ..special { 
  color: blue; 
} 

Types of selectors

There are a few different groupings of selectors, and knowing which type of selector you might need will help you to find the right tool for the job. In this article's subarticles we will look at the different groups of selectors in more detail.

Type, class, and ID selectors

This group includes selectors that target an HTML element such as an <h1>.

h1 { }

It also includes selectors which target a class:

.box { }

or, an ID:

#unique { }

Attribute selectors

This group of selectors gives you different ways to select elements based on the presence of a certain attribute on an element:

a[title] { }

Or even make a selection based on the presence of an attribute with a particular value:

a[href="https://example.com"] { }

Pseudo-classes and pseudo-elements

This group of selectors includes pseudo-classes, which style certain states of an element. The :hover pseudo-class for example selects an element only when it is being hovered over by the mouse pointer:

a:hover { }

It also includes pseudo-elements, which select a certain part of an element rather than the element itself. For example, ::first-line always selects the first line of text inside an element (a <p> in the below case), acting as if a <span> was wrapped around the first formatted line and then selected.

p::first-line { }

Combinators

The final group of selectors combine other selectors in order to target elements within our documents. The following for example selects paragraphs that are direct children of <article> elements using the child combinator (>):

article > p { }

Next steps

You can take a look at the reference table of selectors below for direct links to the various types of selectors in this Learn section or on MDN in general, or continue on to start your journey by finding out about type, class, and ID selectors.

Reference table of selectors

The below table gives you an overview of the selectors you have available to use, along with links to the pages in this guide which will show you how to use each type of selector. I have also included a link to the MDN page for each selector where you can check browser support information. You can use this as a reference to come back to when you need to look up selectors later in the material, or as you experiment with CSS generally.

Selector Example Learn CSS tutorial
Type selector h1 {  } Type selectors
Universal selector * {  } The universal selector
Class selector .box {  } Class selectors
id selector #unique { } ID selectors
Attribute selector a[title] {  } Attribute selectors
Pseudo-class selectors p:first-child { } Pseudo-classes
Pseudo-element selectors p::first-line { } Pseudo-elements
Descendant combinator article p Descendant combinator
Child combinator article > p Child combinator
Adjacent sibling combinator h1 + p Adjacent sibling
General sibling combinator h1 ~ p General sibling

In this module

  1. Cascade and inheritance
  2. CSS selectors
  3. The box model
  4. Backgrounds and borders
  5. Handling different text directions
  6. Overflowing content
  7. Values and units
  8. Sizing items in CSS
  9. Images, media, and form elements
  10. Styling tables
  11. Debugging CSS
  12. Organizing your CSS