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Em: When div is nested, em is always scaled to the current div font size.
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Rem: Scales according to the font size of the root node.
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Vh: When height:100vh is set, the visible height of the screen is considered 100vh. The difference is that 100% is scaled as a percentage of the size of its parent element.
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Vw: When width: 100vw is set, the principle is the same as above.
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Vmax: The larger relative to the width or height of the window. The largest of these is divided into 100 units of Vmax;
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Vmin: The smaller of the width or height of the window. The smallest one is divided into 100 units of vmin;
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Viewport refers to the size of the viewable area inside the browser,
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The window. The innerWidth/window. InnerHeight size, does not contain the task bar at the bottom of the title bar and toolbar browser area size.
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Calc is a function provided by CSS3 that evaluates values in CSS files: () Separated by Spaces, for example: width: calc(100%-10px); Any length value can be computed using the calc() function; Calc () supports “+”, “-“, “*”, “/”; The calc() function uses standard mathematical precedence rules; Calc (100vh-10px) represents the size of the entire browser window minus 10px