在根级别使用时，rems 和 ems 是否等效？
Are rems and ems equivalent when used at root level?
来自 我看到规范中 rem 的定义是什么：
rem unit
Equal to the computed value of font-size on the root element. When specified in the font-size property of the root element, or in a document with no root element, 1rem is equal to the initial value of the font-size property.
而em的定义是：
em unit
Equal to the computed value of the font-size property of the element on which it is used.
对我来说，这意味着 1em == 1rem 在 :root 中使用时的定义。
我说得对吗？
是
:root {
font-size:40px;
border-top: 1rem solid red;
border-bottom:1em solid green;
}
来自 rem 的定义是什么：
rem unit
Equal to the computed value of
font-sizeon the root element. When specified in thefont-sizeproperty of the root element, or in a document with no root element,1remis equal to the initial value of thefont-sizeproperty.
而em的定义是：
em unit
Equal to the computed value of the
font-sizeproperty of the element on which it is used.
对我来说，这意味着 1em == 1rem 在 :root 中使用时的定义。
我说得对吗？
是
:root {
font-size:40px;
border-top: 1rem solid red;
border-bottom:1em solid green;
}