How to define css

CSS, the full name of Cascading Style Sheets, is a style sheet language used to add styles to documents such as HTML. CSS can control the font, color, spacing and other styles of text, as well as the size, position, background and other styles of elements. The main function of CSS is to separate content and style, separate the structure and style of web pages, and improve the maintainability and readability of web pages.

The syntax defined by CSS is very flexible. You can use attributes and values ​​to define styles. It also supports the use of selectors and pseudo-classes to define different styles for different elements or states.

In CSS, you can use selectors to locate elements in HTML to specify styles for these elements. Selectors can be element names, class names, IDs, attributes, and many combinations. For example, you can use the following code to define a class for setting the style of a specific element:

.my-class {
    font-size: 16px;
    color: #333333;
}

In this code, .my-class is a class selector, which means defining a A class named my-class, and set the font size to 16 pixels and the color to #333333 for all elements under this class. In HTML code, you can apply this class to a specific element, for example:

<div class="my-class">这是一段文本</div>

At this time, this text will use the font size and color defined in the style.

In addition to using class selectors, CSS also supports using multiple selectors such as ID selectors and element selectors to locate elements. For example, the following code can define styles for a specific element with the ID content:

#content {
    font-size: 18px;
    color: #666666;
}

In HTML code, you can use this ID selector like this:

<div id="content">这是一段文本</div>

This way, the text will use the font size and color defined in the style.

In CSS, you can also use pseudo-classes to locate different states of elements, such as when the mouse is hovering over the element. The following code can set the background color of an element to gray when the mouse is hovering over it:

a:hover {
    background-color: #cccccc;
}

In HTML code, you can define a link like this and apply the above style to this link:

<a href="#" class="my-link">这是一个链接</a>

In this way, when the mouse hovers over this link, the background color of the link will change to gray.

In short, the definition of CSS is very flexible. Using selectors and pseudo-classes, you can define different styles for different states of specific elements, thereby adding more cool visual effects to documents such as HTML. Therefore, learning and mastering CSS is an essential skill for modern web development.

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