CSS Basics - Selector Advanced, Background Related Properties (Color/Image)

Goal: Be able to understand the rules of compound selectors and use compound selectors to select elements in HTML

Learning path:
		1. compound selector
		2. union selector
		3. intersection selector
		4. hover pseudo class selector
		5. Emmet grammar

What we have learned this time:

1. Advanced selector

1.1 Descendant selector: space

➢ Function: According to the nesting relationship of HTML tags, select elements that meet the conditions in the descendants of the parent element

➢ Selector syntax: selector1 selector 2 { css }

➢ Result:

• Among the descendants (son, grandson, great-grandson...) of the label found by selector 1, find the label that satisfies selector 2 and set the style

➢ Points to note:

\1. Offspring include: son, grandson, great-grandson...

\2. In the descendant selector, the selector is separated from the selector by a space

1.2 Child selector:

➢ Function: According to the nesting relationship of HTML tags, select the element that satisfies the condition in the child of the parent element

➢ Selector syntax: selector1 > selector 2 { css }

➢ Result:

• Among the children (sons) of the label found by selector 1, find the label that satisfies selector 2 and set the style

➢ Points to note:

\1. Children only include: son

\2. In the child selector, the selector is separated from the selector by >

2.1 Union selector:,

➢ Function: Select multiple groups of labels at the same time and set the same style

➢ Selector syntax: selector1, selector 2 { css }

➢ Result:

• Find the label selected by selector 1 and selector 2, and set the style

➢ Points to note:

\1. Each group of selectors in the union selector is separated by ,

\2. Each set of selectors in the union selector can be a basic selector or a compound selector

\3. Each group of selectors in the union selector is usually written one per line to improve the readability of the code

3.1 Intersection selector: right next to

➢ Function: Select tags that satisfy multiple selectors in the page at the same time

➢ Selector syntax: selector 1 selector 2 { css }

➢ Result:

• (both in principle) Find the label that can be selected by both selector 1 and selector 2 in the page, and set the style

➢ Points to note:

\1. The selectors in the intersection selector are next to each other, and there is no separation

\2. If there is a label selector in the intersection selector, the label selector must be written at the top

4.1 hover pseudo class selector

➢ Function: select the state when the mouse is hovering over the element, and set the style

➢ Selector syntax: selector:hover { css }

➢ Points to note:

\1. A certain state of the element selected by the pseudo-class selector

5.1 emmet syntax --- quickly generate code through abbreviated syntax

Quick code generation:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            /* font-size: ; */
            font-size: ;
            /* Prompt css attribute: the first letter of the word */
            /* font-weight: ; */
            font-weight: 700;
            width: ;
            height: ;
            /* background-color: ; */
            background-color: #fff;
            /* line-height: ; */
            line-height: ;

            /* The width is 300, the height is 200, and the background color is pink */
            /* w300+h200+bgc */
            width: 300px;
            height: 200px;
            background-color: pink;
        }

    </style>
</head>
<body>
    <div></div>
    <h1></h1>

    
    <!-- generate div with class name -->
    <div class="box"></div>
    <p class="box"></p>


    <div id="box"></div>
    <p id="box"></p>

    <p class="red" id="one"></p>

    <!-- div at the same level p  + -->
    <div></div>
    <p></p>
    
    <!-- Father and son > -->
    <div>
        <p></p>
    </div>

    <ul>
        <li></li>
    </ul>

    <!-- ul there are 3 li  *Multiplication sign -->
    
    <ul>
        <li></li>
        <li></li>
        <li></li>
    </ul>

    <!-- ul There are 3 inside li, li It has the text 111 inside   {Word} -->
    <!-- ul>li{111}*3 -->
    <ul>
        <li>111</li>
        <li>111</li>
        <li>111</li>
    </ul>

    <!-- ul there are 3 li, li text 1, 2, 3 -->
    <!-- ul>li{$}*3 -->
    <ul>
        <li>1</li>
        <li>2</li>
        <li>3</li>
    </ul>
</body>
</html>

2. Context related attributes

Goal: To be able to use background-related properties to decorate the background style of an element

Learning path:
	1. background color
	2. Background picture
	3. background tiling
	4. background position
	5. Linking of background related attributes

1.1 Background color

test:

summary

➢ What is the property name of the background color property?
	• background-color
➢ What is the default attribute value of the background color attribute?
	• transparent: rgba(0,0,0,0),transparent