1. New features of HTML5

The new features of HTML5 are mainly aimed at the previous deficiencies, adding some new tags , new forms and new form attributes , etc.

1. New semantic tags in HTML5

Attributes	describe
autoplay	Video ready to autoplay
controls	Display playback controls to the user
width	Set player width
height	Set player height
loop	Whether to continue playing the video after playing, loop
preload	Specifies whether to preload the video
src	Video Url address
poster	Loading waiting screen picture
muted	Mute playback

Attributes	describe
autoplay	Audio ready to autoplay
controls	Display playback controls to the user
loop	Whether to continue playing the audio after playing, loop
src	Audio Url address

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n can be numbers, keywords and formulas
If n is a number, it is to select the nth child element, and the number inside starts from 1
n is a keyword: even even, odd odd

official	value
2n	even
2n+1	odd number
5n	5 10 15
n+5	From the 5th (including the fifth) to the end
-n+5	The first 5 (including the 5th)

the difference:

nth-child sorts and selects all children in the parent element (the sequence number is fixed) first find the Nth child, and then see if it matches E
nth-of-type sorts and selects the specified child elements in the parent element, first matches E, and then finds the Nth child according to E

selector	Introduction
::before	Insert content before inside the element
::after	Insert content after the inside of the element

Notice:

before and after create an element, but are inline elements
This newly created element cannot be found in the document tree, so we call it a pseudo-element
Syntax: element::before{}
before and after must have a content attribute
before creates an element before the content of the parent element, and after inserts the element after the content of the parent element
Pseudo-element selectors are the same as label selectors , with a weight of 1