The outline is a line around the elements. It is the part of OUTSIDE the borders. The outline property is used to make the element stand out.
 
CSS has the following outline properties:
{outline-color : orange;}                  
property          value 
 
<!DOCTYPE html>
<html>
<body>
<p style="outline-style:orange;">
    TDB Tutorials
</p>
</body>
</html>
If we want to change the style of the outline of an HTML element we can use the CSS3 outline style Property.
 
{outline-style : solid;}
property         value 
 
<!DOCTYPE html>
<html>
	<head>
		<style>
		.tdb-school{
			background-color:white;
			padding:10px 35px;
			border-style:dotted;
			border-radius:5px}
		</style>
	</head>
	<!--Body-->
	<body>
		<button type="submit" class="tdb-school">
		button border properties
		</button>
	</body>
</html>
If you don't want to write different CSS rules for Outline property then you can use Outline Shorthand property.
{outline : color style width}
property        value 
 
<!DOCTYPE html>
<html>
	<!--Body-->
	<body>
		<button type="submit" class="tdb-school"
		style="outline:orange dotted 5px;
		padding:10px 35px;border:solid red 5px">
		button outline property
		</button>
	</body>
</html>