The border-width shorthand CSS property sets the width of an element's border.
|Initial value||as each of the properties of the shorthand:border-top-width: mediumborder-right-width: mediumborder-bottom-width: mediumborder-left-width: medium|
|Applies to||all elements. It also applies to ::first-letter.|
Defines the width of the border, either as an explicit nonnegative
or a keyword. If it's a keyword, it must be one of the following values:
A thin border
A medium border
A thick border
Note: Because the specification doesn't define the exact thickness denoted by each keyword, the precise result when using one of them is implementation-specific. Nevertheless, they always follow the pattern thin ≤ medium ≤ thick, and the values are constant within a single document.