According to W3C specifications, Rem sizing refers to measured font measurement and transformation in proportion to a base font-size.
According to the W3C spec the definition for one rem unit is: \n Equal to the computed value of font-size on the root element. When specified on the font-size property of the root element, the rem units refer to the property’s initial value.
This means that 1rem equals the font size of the html element (which for most browsers has a default value of 16px).
According to the W3C spec the definition for one rem unit is: Equal to the computed value of font-size on the root element. When specified on the font-size property of the root element, the rem units refer to the property’s initial value.
The main problem with em units is that they are relative to the font size of their own element. As such they can cascade and cause unexpected results. Let’s consider the following example, where we want lists to have a font size of 12px, in the case where the root font size is the default 16px: