An entry-level understanding of the CSS knowledge system

Let me share the CSS system diagram. It is very useful. Please save it. The following article will introduce you to the introductory knowledge of CSS.

CSS system

css You can have a rough understanding of the following:

CSS3

##Cascading Style SheetCascading Cascading Style Sheet

Font , color, margin, height, width, background image, web page positioning, web page floating...

css selector (emphasis)

Beautify the web page (text, shadow, hyperlink, list, gradient )

Box model

Floating, positioning

Web page animation

Advantages of css;

1. Separation of content and performance

2. The web page structure is unified and can be reused

3. The styles are very rich

4. It is recommended to use css files independent of html

5 , Use SEO to easily be included by search engines!

1. Selector

1. Select a certain item on the page One or a certain type of element

Basic selector
• 
  
• Tag selector

• Class selector

• id selector

• Level selector

• Descendant selector: After an element

body p{ background: #c56b22; }

2. Sub-selector

/*子选择器，只选择向下一代*/ body>p{ background: deepskyblue; }

3. Adjacent sibling selector

/*相邻兄弟选择器，只有一个，向下*/ .active + p{ background: orange; }

4.Universal selector

/*通用兄弟选择器，当前选中元素的向下的所有元素*/ .active~p{ background: aquamarine; }

2. Pseudo-class selector

/*ul的第一个子元素*/ ul li:first-child{ background: #c56b22; } /*ul的最后一个子元素*/ ul li:last-child{ background: aqua; } /*选中p1,定位到父元素，选择当前的第一个元素 选择当前p元素的符集元素，选择符父级素的第一个，并且是当前元素才生效 */ p:nth-child(1){ background: antiquewhite; } /*选中父元素，下的p元素的第二个，按类型*/ p:nth-of-type(2) { background: #b04a6f; }

3. Beautify the web page

1. Font style

2. Text style

Color
1. color rgb rgba
Text alignment
2. text-align=center
First line indent
3. text-indent:2em
行高
4. line-height:Single line text is centered up and down!
Decoration
5. text-decoration:
Text image horizontal alignment:
6. /middleis vertical/vertical-align: middle;

3. Shadow

  
 ¥30 
 

4. Hyperlink pseudo-class

     
 《从0到1开启商业与未来的秘密》 
 
 作者：[美] 彼得·蒂尔，布莱克·马斯特斯（Blake Masters）著， 高玉芳 译 
 

5, List

1) Background

• Background color

  
  

• Background image

.title{ font-size: 18px; /*font: oblique bold 20px/30px Arial;*/ font-weight: bold; text-indent: 1em; line-height: 35px; /*background: #fcb4dc;*/ /*颜色、图片、位置、平铺方式*/ background: #fcb4dc url("../image/d.jpeg") 250px 4px no-repeat; } ul li{ /*行高*/ height: 30px; list-style: none; text-indent: 1em; /*background: url("../image/r.jpeg") 200px 1px no-repeat;*/ background-image: url("../image/r.jpeg"); background-repeat: no-repeat; background-position: 200px 1px; }

2) Gradient

background-color: #A9C9FF; background-image: linear-gradient(60deg, #A9C9FF 0%, #FFBBEC 100%);

3) Box model

• Border

• Inner and outer margin

• Rounded border

## Shadow
• Floating

4) Parent border collapse problem

/* clear:right; 右侧不允许又浮动元素 clear:lerf; 左侧不允许有浮动元素 clear:both; 两侧不允许有浮动元素 clear:none; */

Solution:

Increase the height of the parent element

#father{ border:1px #000 solid; height:800px}

1. Add an empty p tag and clear the floating

2. .clear{ clear:both; margin:0; padding:0;}

overflow

#在父级元素中添加一个 overflow:hodden;

3. Add a pseudo-class

   #father:after{ content:''; display:block; clear:both;}

   to the parent class
4. If it floats, it will break away from the standard document flow, so we need to solve the problem of parent border collapse

6. Positioning

Relative positioning

• Specify offset relative to the original position, relative positioning If so, it will still be in the standard document flow! The original position will be retained
  position:relative

  
  

  top:-20px; left:20px; bottom:-10px; right:20px;

Absolute positioning

• position:absolute
  

  定位:基于xxx定位，.上下左右~ 1、没有父级元素定位的前提下，相对于浏览器定位 2、假设父级元素存在定位,我们通常会相对于父级元素进行偏移~ 3、在父级元素范围内移动 相对于父级或浏览器的位置，进行指定的偏移,绝对定位的话，它不在标准文档流中，原来的位置不会被保留

Fixed positioning

• 
  position:fixed

  
  

z-index
• Level, the default is 0, the highest is unlimited

  
  

  /*背景透明度,或者使用rgba，早期版本filter:alpha(opacity=50)*/ opacity:0.5 /*filter:alpha(opacity=50)*/

Recommended learning:

CSS video tutorial

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