This property is a shorthand property for setting 'border-width-top', 'border-width-right', 'border-width-bottom' and 'border-width-left' at the same place in the style sheet.

There can be from one to four values, with the following interpretation:

• one value: all four border widths are set to that value
• two values: top and bottom border widths are set to the first value, right and left are set to the second
• three values: top is set to the first, right and left are set to the second, bottom is set to the third
• four values: top, right, bottom and left, respectively

In the examples below, the comments indicate the resulting widths of the top, right, bottom and left borders:

      H1 { border-width: thin }                   /* thin thin thin thin */
      H1 { border-width: thin thick }             /* thin thick thin thick */
      H1 { border-width: thin thick medium }      /* thin thick medium thin */
      H1 { border-width: thin thick medium thin } /* thin thick medium thin */
      

Border widths cannot be negative.