CSS selectors mainly include basic selectors, combination selectors, attribute selectors, pseudo-classes and pseudo-element selectors. 1. The basic selector includes elements, classes, IDs, and wildcard selectors, which are used for basic style settings. 2. The combination selector contains descendants, child elements, adjacent brothers, and general brother selectors, which are used to handle element structure relationships. 3. The attribute selector matches elements based on attributes and is suitable for specific element control such as forms and links. 4. Pseudo-class and pseudo-element selector are used to control states and generate content, such as:hover, ::before, ::after, etc., to improve interaction and decorative effects.

The CSS selector is a very core part of front-end development, used to accurately select elements in the page and thus apply styles. Understanding different types of selectors can help you write CSS more efficiently, reduce redundant code, and better control the priority and scope of styles.

1. Basic selectors: the most commonly used and most basic

This type of selector is the most commonly used when writing CSS every day, including:

• Element selector (such as div , p ): directly select elements based on the HTML tag name.
• Class selector (such as .class-name ): Select one or more elements by the class attribute value.
• ID selector (such as #id-name ): Select a specific element by a unique id, note that the id in a page should be unique.
• Wildcard selector ( * ): Match all elements, often used to reset the default style.

These selectors are simple but practical and are suitable for most basic style settings.

2. Combination selector: Combine multiple selectors for more precise matching

Sometimes we need to apply styles to elements under certain structures, and then we can use the combination selector:

• Descendant selector (such as div p ): Select all p elements inside the div, no matter how deep the nesting is.
• Children element selector (such as div > p ): Only the direct child element p of the div is selected.
• Adjacent brother selector (such as h1 p ): Select the p element immediately after h1.
• Universal sibling selector (such as h1 ~ p ): Select all p elements of the same level after h1.

These selectors are particularly suitable for situations in layout where relationships between elements need to be handled, such as content paragraphs after the title of the article.

3. Attribute selector: matches the attributes of the element

When you want to style according to HTML attributes, the property selector comes in handy:

• [type] : Select the element with the type attribute.
• [type="text"] : Select the element with type "text".
• [class~="btn"] : Select the element containing "btn" in the class.
• [href*="example"] : Select the link containing "example" in href.

This selector is very useful when dealing with elements with specific attributes, such as forms, links, images, etc.

4. Pseudo-class and pseudo-element selector: for state and content style control

Instead of selecting the actual DOM node, this type of selector selects a certain state or generates content:

• Pseudo-classes :

  • :hover : The status when the mouse is hovered.
  • :active : When the element is activated (such as click).
  • :focus : When the element gets focus.
  • :nth-child(n) : Select the nth child element.

• Pseudo-elements :

  • ::before and ::after : Insert content before and after the element.
  • ::first-line : Select the first line of the text block.
  • ::placeholder : Select the placeholder text in the input box.

Pseudo-classes are mostly used to change the interactive state, while pseudo-elements are often used to add decorative content.

Basically these common types. Although it seems a lot, many of them are naturally used in actual projects. The key is to understand the differences and applicable scenarios between them, so that the written CSS will be both concise and effective.

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