This CSS Border Online Test helps you to Boost your Knowledge in PHP. We Always declare the border-style property before the border-width property. An element must have borders before you can set the width. One of the CSS property border-bottom-left-radius CSS property that is used to define rounded corners on the left side of the bottom border of a box. Another border-bottom-width property is used to set the width of the bottom border of an element. The width of the border can be explicitly set using a value, or by using one of three border width keywords: thin, medium, and thick.