i have been trying to learn CSS for a while. since its easy for me i tried using CSS in the document. but now i realised if i want to custermise it later i have a problem. is this the reason why css is used as external file
Hello marzooq, there are two main reasons why to use an external CSS file: 1) You will save an internet traffic, because in case of external CSS file, browser will download this file only once, but in case of embedged CSS file browser will download the definitions always. 2) If you have for example 20 static html files with an embedged CSS definitions and you want to make some changes, you must edit each of all 20 html files, instead of edit just 1 external CSS file. (that's what you are talking about) Hope this informations helps.
External CSS may also help in terms of SEO by giving you an optimal code to content ratio but that is up for debate. smalldog covered the two most important points imo.
Actually it does have a benefit from an SEO standpoint - less code directly in the Web page for the spider to go through.
Yes, light web pages with external stylesheets good for SEO and convenient when you want to change the overall theme of your site with just editing one file...