The difference between EM and REM

1. px It's fixed pixels , Once set, it cannot be changed because it adapts to the page .
2. em yes rem be relative to px More flexibility , They change with respect to the unit of length , More suitable for responsive layout .

em Relative to the parent element
rem Relative to the root element

em Specific analysis of ：

Sub element font size of em Is the font size relative to the parent element
Elemental width/height/padding/margin use em Relative to the element font-size.

rem Specific analysis ：

rem Is that the whole length is equivalent to the root element , Who is the root element ？ Elements
The usual way is to give html Element to set a font size , Then the length unit of other elements is rem.

html {
    
        font-size: 10px;
}