You can specify the width of the border through the border-width property.
There are two ways to specify the width of the border: you can specify a length value, such as 2px or 0.1em (units are px, pt, cm, em, etc.), or use one of the 3 keywords, which are thick, medium (Default) and thin.
Note: CSS does not define the specific width of the 3 keywords, so one user may set thick, medium, and thin to be equal to 5px, 3px, and 2px, respectively, and another user may set them separately. Are 3px, 2px, and 1px.