diff --git a/guide/english/css/fonts/index.md b/guide/english/css/fonts/index.md
index e510f22ba7..6edd47bc4f 100644
--- a/guide/english/css/fonts/index.md
+++ b/guide/english/css/fonts/index.md
@@ -62,9 +62,10 @@ The `font-size` property sets the size of the text. The default size is usually
 
 There are several different values that may be used to determine size:
 
-* `px` (pixels) - specifies the exact number of pixels for the size of the font
-* `em` - a relative measurement that is dynamically created based on the font size of an element's parent. `1em` = the current font size, so `1em` = `16px` (recommended by the W3C)
-* `small`, `medium`, `large` - absolute size values
+* `px` (pixels) - The default size of text being `16px`
+* `em` - `1em` = the current font size, so `1em` = `16px` (recommended by the W3C)
+* `rem` (root em) - The value of the font size of the root element `html`. Whereas `em` units are relative to the font size of their parent element, `rem` units are always relative to the document's root element.
+* `small`, `medium`, `large` - known as absolute size values
 * `%` - percentages
 
 ```css