The ‘outline-width’ property specifies the width for the outline of an element.
The outline properties create a uniform line around an object in order to draw visual attention. An outline is slightly different than a border in several ways: An outline is drawn starting “just outside the border edge” and is allowed to be non-rectangular. Outlines are always rendered on TOP of an element’s rendering box and do not influence the box’s position or size calculation; the document does not need to be re-flowed when a border is rendered or hidden, but the outline may overlap other nearby elements
<input type="text" name="test" value="some text"
inherit: Explicitly sets the value of this property to that of the parent
thin | medium | thick: Renders a “thin”, “medium” or “thick” outline border for the element’s rendering box. The actual thickness of these outline values is not specified, but “thin” should have a smaller thickness than “medium”, which should have a smaller thickness than “thick”
[length]: Sets the width of the outline around the current element rendering box to an explicit measurement