How to use CSS

CSS is a very important technology in web design. Through it, we can change the style and layout of web pages to make them look more beautiful and easier to read. In this article, we will introduce the basic syntax of CSS and some commonly used style properties to help beginners understand how to use CSS.

1. Basic grammar of CSS

Before using CSS, we need to understand some basic grammar rules. The syntax structure of CSS consists of three parts: selector, attribute and value, as shown below:

选择器 {
    属性1: 值1;
    属性2: 值2;
    属性3: 值3;
}

Among them, the selector is used to specify the HTML element to be styled, the attribute is used to describe the characteristics to be changed, and the value is the attribute value to be changed. Use a colon (:) to separate each attribute from its value, and separate each attribute from its value with a semicolon (;). There is no need to add a semicolon at the end of the last attribute.

For example, to change the text color of all paragraphs (p) in HTML to red, you can use the following CSS style:

p {
    color: red;
}

2. CSS style attributes

In CSS, there are many properties that can be used to modify the visual style of a web page. The following are some commonly used style properties.

1. Font attributes

• font-size: font size, the unit can be pixels (px), percentage (%) or em, etc.
• font-family: font name, which can be a common English font or Chinese font.

For example:

p {
    font-size: 16px;
    font-family: "Microsoft Yahei", Arial, sans-serif;
}

2. Text attribute

• color: font color.
• text-align: Text alignment, which can be left, right, center or justify, etc.

For example:

p {
    color: #333;
    text-align: center;
}

3. Background attribute

• background-color: background color.
• background-image: background image.
• background-repeat: Whether the background image is repeated, it can be repeat, repeat-x, repeat-y or no-repeat, etc.
• background-position: background image position, which can be left top, center center, right bottom, etc.

For example:

body {
    background-color: #fff;
    background-image: url(bg.jpg);
    background-repeat: no-repeat;
    background-position: center center;
}

4. Border attribute

##border-width: border width.
• border-style: Border style, which can be solid, dashed, dotted or double, etc.
• border-color: border color.

For example:

div {
    border-width: 1px;
    border-style: solid;
    border-color: #ccc;
}

Box model attributes

##width: element width.

• height: Element height.
• padding: padding.
• margin: Margin.
• For example:

div {
    width: 200px;
    height: 150px;
    padding: 10px;
    margin: 20px;
}

3. CSS selector

CSS selector is a pattern used to match HTML elements and can be used to set styles for specific elements. . Below are some commonly used selectors.

Element selector

1. The element selector can match any element in HTML, such as p, div, h1, etc.

For example:

p {
    color: #333;
}

Class selector

2. The class selector starts with a period (.) and can be specified for multiple elements in HTML style.

For example:

.highlight {
    background-color: yellow;
}

ID selector

3. The ID selector starts with a pound sign (#) and is used to match unique HTML elements.

For example:

#logo {
    width: 100px;
    height: 80px;
}

Descendant selector

4. Descendant selector can match elements nested inside other HTML elements, separated by spaces ( ) Different selectors.

For example:

#nav li {
    display: inline-block;
}

Adjacent sibling selector

5. The adjacent sibling selector can match the sibling element immediately following the previous specified element, use plus sign ( ) to indicate.

For example:

h1 + p {
    font-size: 14px;
}

4. CSS style inheritance

CSS styles can be passed to its child elements through inheritance. When a parent element sets a certain style, its child elements will automatically inherit that style, unless the child element sets its own style.

For example:

body {
    font-size: 16px;
    color: #333;
}

In this example, all HTML elements will automatically inherit the font size and color.

Conclusion

Through the introduction of this article, beginners can use CSS to change the style and layout of web pages. Although there are many CSS properties and selectors available, understanding its basic syntax and common style properties is basic. Through continuous learning and practice, you will become more proficient in using CSS and create more complex web designs.

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