A
stylesheet
is a set of CSS rules used to control the layout and design of a webpage or document.
Internal
stylesheets are placed inside a
<style>
element inside the
<head>
of a web document, and
external
stylesheets are placed inside a separate
.css
file, which is applied to a document by referencing the file inside a
<link>
element in the document's head.
External stylesheets are generally preferred because they allow you to control the styling of multiple pages from a single place, rather than having to repeat the CSS across each page.