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 {
outline-width: thin
}