How to use css

CSS (Cascading Style Sheets) is a language that can add style, layout and design to web pages. CSS is a very popular programming language that can add various looks and features to web pages, such as fonts, colors, spacing, backgrounds, animations, etc. In this article, we’ll take a deep dive into using CSS to help you better master it during web development.

1. How to introduce CSS

Before learning CSS, you first need to understand how to introduce CSS into your HTML file. CSS style sheets can be introduced in three different ways:

1. Inline style sheets

Inline style sheets are defined by using style attributes in tags. For example, in an HTML file you could write:

This is a paragraph with an inline style sheet.

2. Internal style sheet

Define an internal style sheet by using the <style></style> tag in the HTML file. For example:

<title>内部样式表</title>
<style>
    body {
        background-color: grey;
        color: white;
        font-size: 20px;
    }
    h1 {
        color: red;
        font-size: 32px;
    }
</style>

<h1 id="这是一个内部样式表的标题">这是一个内部样式表的标题</h1>
<p>这是一个带有内部样式表的段落。</p>

3. External style sheet

By using the <link> tag in the HTML file Link to an external style sheet. For example:

<title>外部样式表</title>
<link rel="stylesheet" href="style.css">

<h1 id="这是一个外部样式表的标题">这是一个外部样式表的标题</h1>
<p>这是一个带有外部样式表的段落。</p>

Note: When using an external style sheet, the linked style sheet file must be in the same directory as the HTML file, and the file extension The name must be .css.

2. CSS syntax

CSS syntax is very simple and mainly consists of the following parts:

1. Selector

The selector is used to specify The HTML element to apply the style to. For example, the following code specifies a style for the select title element:

h1 {

color: red;
font-size: 32px;

}

2. Attributes The

attribute specifies the style to apply. Style type. For example, the following attributes specify the color and font size of the title element:

color: red;
font-size: 32px;

3.Value

value specifies The specific value of the attribute. For example, the following code specifies a font-size of 32 pixels for the title element:

font-size: 32px;

Note: CSS properties are not limited to these, there are many other properties used More CSS style control.

3. Common CSS style properties

The following are some common CSS style properties, you can use them when applying styles:

1. Background color (background- color)

background-color attribute is used to specify the background color of the element. For example:

background-color: red;

2. Font color (color)

color attribute is used to specify the font color of the element. For example:

color: white;

3. Text alignment (text-align)

The text-align attribute is used to specify the alignment of text in an element. For example:

text-align: center;

4. Font size (font-size)

font-size attribute is used to specify the size of the element font. For example:

font-size: 20px;

5. Border

You can add a border to an element by adding the border attribute. For example:

border: 1px solid black;

Note: The value of the border attribute includes: border width, border style and border color.

6. Width (width)

The width attribute is used to specify the width of the element. For example:

width: 50%;

7. Height (height)

The height attribute is used to specify the height of the element. For example:

height: 100px;

8. Padding (padding)

The padding attribute is used to specify the padding of the element. For example:

padding: 10px;

9. Margin (margin)

The margin attribute is used to specify the margin of the element. For example:

margin: 10px;

4. CSS selectors

In addition to the above basic style attributes, there are many different selector types that can help you Refine the style. The following are some of the most common selectors:

1. Class selector (class selector)

The class selector is used to select elements with the same class name. For example:

<title>类选择器</title>
<style>
    .selected {
        background-color: red;
        color: white;
    }
</style>

<p class="selected">这个段落被选中了。</p>
<p>这个段落没有被选中。</p>
<p class="selected">这个段落也被选中了。</p>

2. Tag selector (tag selector)

The tag selector is used to select all elements with the same tag name . For example:

<title>标签选择器</title>
<style>
    p {
        color: red;
    }
</style>

<p>这是第一个段落。</p>
<p>这是第二个段落。</p>
<p>这是第三个段落。</p>

3.id selector (id selector)

The id selector is used to select unique elements with a specified ID. For example:

<title>id 选择器</title>
<style>
    #header {
        color: red;
        font-size: 24px;
    }
</style>

<h1 id="这是顶部标题">这是顶部标题</h1>
<p>这是一个段落。</p>

4. CSS inheritance

CSS 样式是可以从父元素继承到子元素的。例如，如果在 body 元素上应用了一个背景颜色，那么所有的子元素（如段落、标题等）都将继承该背景颜色。例如：

<title>继承性</title>
<style>
    body {
        background-color: grey;
        color: white;
        font-size: 20px;
    }
    h1 {
        color: red;
        font-size: 32px;
    }
</style>

<h1 id="这是标题">这是标题1</h1>
<p>这是一个段落。</p>
<h2 id="这是标题">这是标题2</h2>
<p>这是另一个段落。</p>

五、CSS的优先级

当多个样式应用到同一元素上时，CSS 样式有许多不同的规则来决定哪些样式结合在一起。以下是一些有关优先级的规则：

1.行内样式表的优先级最高

如果在元素上应用行内样式表，则行内样式表的样式将优先于内部或外部样式表。

2.选择器特殊性

如果选择器特殊性相同，则会根据选择器的出现位置决定优先级。例如，内部样式表的样式比外部样式表的样式更优先。

3.样式继承

当两个或多个样式同时应用于一个元素，且它们都是通过继承方式获得的，则优先选取本身的样式。

4.重载样式

如果两个样式在元素上应用，但具有相同的选择器和特殊性，则最后应用的样式将优先于其他样式。

六、总结

在本文中，我们已经深入了解了 CSS 的使用方法，包括引入样式表、基本 CSS 语法、常见样式属性、选择器、继承性和优先级。这些基本的 CSS 知识应该对您在网页开发中的样式和布局决策有所帮助。随着您的使用和实践，您会发现更多的 CSS 功能和方法，以及如何利用它们来创造出更好的网页设计。

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