border: 2px solid #45834;
box-shadow: 2px 2px 3px #888888;
margin: 0 0 10px 10px;
Cascading Stylesheets are used to modify the appearance of web pages. Most often referred to as CSS, these files are loaded along with the other documents to give instructions to the browser on what fonts to use, what colors, width and height of various elements, borders, backgrounds and a host of other features.
Why use CSS for your web pages?
Using a stylesheet rather than inline styling or a <style> section at the top of your HTML document allows you to standardize the look across your entire site with one file.
Having centralized styling also allows you to make changes easily that will be reflected on every page that uses that particular style sheet.
How to add a style sheet to your web page
To use a style sheet, you must tell the browser the location and name of the stylesheet with a line inside the <head> section of your HTML document.
<link type="text/css" href="css/layout.css" rel="sylesheet"/>
This <link> tag must be added to every page on your site that will be using the styles from that style sheet.
You can have multiple style sheets added to a web page, but each style sheet must have its own <link> tag and own unique file name. Style sheets later in the list in the HTML document will override any duplicate styles in earlier style sheets.