what is css

css is a cascading style sheet, which is a computer language used to express file styles such as html or xml. CSS can perform pixel-level precise control over the layout of element positions in web pages, supports almost all font sizes and styles, and has the ability to edit web page objects and model styles.

The operating environment of this article: windows10 system, css 3, thinkpad t480 computer.

The concept of css:

Cascading Style Sheets (full English name: Cascading Style Sheets) is an application used to express HTML (standard universal markup language) or XML (standard A subset of Universal Markup Language) and other document-style computer languages. CSS can not only statically modify web pages, but can also cooperate with various scripting languages ​​to dynamically format various elements of web pages.

CSS can perform pixel-level precise control over the layout of element positions in web pages, supports almost all font size styles, and has the ability to edit web page objects and model styles.

CSS provides a style description for the HTML markup language, defining how elements in it are displayed. CSS is a breakthrough in the field of web design. It can be used to modify a small style to update all page elements related to it.

In general, CSS has the following characteristics:

Rich style definition

CSS provides a rich document style appearance, as well as setting text and The ability of the background attribute; allows you to create a border for any element, as well as the distance between the element border and other elements, and the distance between the element border and the element content; allows you to freely change the capitalization, decoration, and other page effects of text.

Easy to use and modify

CSS can define the style in the style attribute of the HTML element, you can also define it in the header part of the HTML document, or you can declare the style in a special CSS file for reference in HTML pages. In short, CSS style sheets can store and manage all style declarations in a unified manner.

In addition, elements of the same style can be classified and defined using the same style, you can also apply a certain style to all HTML tags with the same name, or you can assign a CSS style to a certain in page elements. If we want to modify the style, we only need to find the corresponding style statement in the style list and modify it.

Multi-page application

CSS style sheet can be stored in a separate CSS file, so that we can use the same CSS style sheet in multiple pages. Theoretically, CSS style sheets do not belong to any page file and can be referenced in any page file. In this way, the styles of multiple pages can be unified.

(Learning video sharing: css video tutorial)

Cascading

Simply put, cascading is to set the same style for an element multiple times. This will use the last property value that was set. For example, if you use the same set of CSS style sheets for multiple pages in a site, and if you want to use other styles for some elements in some pages, you can define a separate style sheet for these styles and apply them to the page. These styles defined later will override the previous style settings, and what you see in the browser will be the style effect set last.

Page Compression

In websites that use HTML to define page effects, a large number or repeated tables and font elements are often required to form text styles of various specifications. The consequence of this is that a large number of HTML tags, thereby increasing the page file size. Putting the style declaration separately in the CSS style sheet can greatly reduce the size of the page, so the time spent loading the page will also be greatly reduced. In addition, the reuse of CSS style sheets reduces the size of the page to a greater extent and reduces the download time.

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