CSS border-bottom-width
The border-bottom-width property sets the width of the bottom border of an element.
This property can have the following values:
thin: the border width is set to a thin linemedium: the border width is set to a medium linethick: the border width is set to a thick linelength: specify the width of the border in pixels, em, rem, etc.
Here is an example of how to use the border-bottom-width property:
The code above sets a solid bottom border with a width of 5 pixels for a <div> element. You can adjust the value of border-bottom-width to change the thickness of the bottom border.