Outline is a line that goes around the element, outside of the border. In contrast to border, outlines do not take any space in the box model. So adding an outline to an element does not affect the position of the element or other elements.

In addition, outlines can be non-rectangular in some browsers. This can happen if outline is applied on a span element that has text with different font-size properties inside it. Unlike borders, outlines cannot have rounded corners.

The essential parts of outline are outline-color, outline-style and outline-width.

The definition of an outline is equivalent to the definition of a border:

An outline is a line around an element. It is displayed around the margin of the element. However, it is different from the border property.

outline: 1px solid black;

The outline-style property is used to set the style of the outline of an element.

p {
  border: 1px solid black;
  outline-color:blue;
  line-height:30px;
}
.p1{
  outline-style: dotted;
}
.p2{
  outline-style: dashed;
}
.p3{
  outline-style: solid;
}
.p4{
  outline-style: double;
}
.p5{
  outline-style: groove;
}
.p6{
  outline-style: ridge;
}
.p7{
  outline-style: inset;
}
.p8{
  outline-style: outset;
}

HTML

<p class="p1">A dotted outline</p>
<p class="p2">A dashed outline</p>
<p class="p3">A solid outline</p>
<p class="p4">A double outline</p>
<p class="p5">A groove outline</p>
<p class="p6">A ridge outline</p>
<p class="p7">An inset outline</p>
<p class="p8">An outset outline</p>