The external style sheet is a .css file that you link to your website,this makes it so that what ever you change in .css sheet ,will effect every page in your website.i.e we are using link external link in html page..
Syntax: <link href="pathname" style="text/css" rel="stylesheet">
An External Style Sheet is a file containing only CSS syntax (no document content or elements) and should carry a MIME type of "text/css." The style information is not explicitly tied directly to the document's elements, so Selector syntax is used to specify what styles attach to which portions of the document tree