With the rapid development of Web technology, CSS has become one of the most critical technologies in web design and development. CSS, Cascading Style Sheets, is used to control the style and layout of web pages. Through CSS, developers can easily adjust the styles on the page, such as fonts, colors, sizes, borders, backgrounds, etc., to make the page more beautiful and the content clearer. So, how to fill in CSS? This article will give you an in-depth understanding of the basic concepts and usage of CSS, and help you master indispensable skills in web design.
1. Basic concepts of CSS
- What is CSS?
CSS is a style sheet language developed by W3C, which is used to describe style and layout information in markup languages such as HTML or XML. CSS can separate the content and appearance of a web page, making it easier for developers to modify the layout and style of a web page without changing the HTML code.
- The role of CSS
CSS is mainly used to control the appearance and style of web pages, such as fonts, colors, sizes, borders, backgrounds, etc. Through CSS, developers can separate the style of web pages from HTML code, making the code clearer and easier to maintain, and also facilitating web design and development work.
- CSS syntax rules
CSS syntax consists of selectors and declaration blocks, where selectors are used to identify tags in HTML, and declaration blocks are used to describe these tags styles and attributes.
For example, in the following code, the selector is h1, which means to style the
tag in HTML, and the color attribute in the declaration block means that the font color is red: h1 {
color: red;
}
2. Common usage of CSS
- How to introduce CSS
CSS can be introduced into HTML documents in two ways: internal style sheets and external style sheets .
- Internal style sheet: Write the CSS code directly in the of the HTML document, as shown below:
<!DOCTYPE html>
<html>
<head>
<title>My Web Page</title>
<style>
h1 { color: red; }
p { font-size: 20px; }
</style>
</head>
<body>
<!-- HTML文档的内容 -->
</body>
</html>- External style sheet: Save the CSS code as a separate file, and then introduce the file in the HTML document using the tag, as shown below:
<!DOCTYPE html>
<html>
<head>
<title>My Web Page</title>
<link rel="stylesheet" href="style.css">
</head>
<body>
<!-- HTML文档的内容 -->
</body>
</html>- CSS selector
CSS selectors are used to select HTML elements that need to be styled. Common selectors include:
- Tag selector (element selector): Select tags in HTML (such as h1, p, img, etc.) for style setting.
- Class selector: Select the class attribute in HTML (such as class="nav") for style setting.
- ID selector: Select the id attribute in HTML (such as id="header") for style setting.
- Descendant selector: Select sub-tags under a certain tag for style setting. For example, div p { color: red; } means selecting all p tags under the div for style setting.
- Child selector: Select the direct child element under a certain tag for style setting. For example, div > p { color: red; } means selecting the p tag of the direct child element under the div for style setting.
For example, in the following code, the class selector .nav and the descendant selector header nav are used to select elements with class nav and all nav tags under the header tag in the page for style setting. :
.nav {
background-color: gray;
color: white;
}
header nav {
font-size: 16px;
}- CSS style attributes
CSS style attributes are used to set the style and appearance of HTML elements. Common attributes include:
- Font style related attributes: font-size (font size), font-family (font type), font-weight (font thickness), color (font color), etc.
- Border style related attributes: border-width (border width), border-style (border style), border-color (border color), etc.
- Background-related attributes: background-color (background color), background-image (background image), background-repeat (background image repetition method), etc.
- Size and position related attributes: width (element width), height (element height), margin (outer margin), padding (inner margin), etc.
For example, in the following code, the font-size, padding and background-color attributes are used to set the font size, padding and background color of the element respectively:
h1 {
font-size: 30px;
padding: 10px;
background-color: #f2f2f2;
}3. CSS optimization and best practices
- Use external style sheets
Writing CSS code in external style sheets can effectively reduce the page loading time. Improve page loading speed. At the same time, it can also make the code clearer, easier to maintain and modify.
- Streamline CSS code
Avoiding the use of redundant and unnecessary attributes in CSS code can greatly reduce the size of CSS files and also help improve the quality of web pages. Loading speed.
- Follow CSS naming conventions
Following CSS naming conventions can make the code clearer and easier to maintain. For example, using semantic class names (such as .nav, .header, and .footer) can better express the meaning and purpose of the element.
- Browser Compatibility
When writing CSS code, you should try to avoid using browser-specific properties and syntax. If you must use browser-specific properties or syntax, you should add the corresponding browser compatibility code (such as -webkit, -moz, etc. prefix) to the code.
Summarize
CSS is one of the indispensable technologies in web design and development. It can help us control the appearance and style of web pages, thereby making the pages more beautiful and the content clearer. This article introduces the basic concepts and common usage of CSS, as well as the optimization and best practices of CSS, hoping to help readers have a deeper understanding and mastery of CSS technology.
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