How to make the height of the div automatically fill the remaining space? What should I do if height:100% does not take effect?

Knowledge point: When the height of an element is set to a percentage, its actual height is expanded by the actual content height , or inherited by the parent element . If the parent element does not have a height set, then the percentage height of the child element has no effect.

Wrong way:

body{
    
    
	height:100%; 
	//虽然body的高度为100%，但是父元素没有高度。
	//所以body的height:100%无效。
}

Correct spelling:

html,body{
    
    
	height:100%;