Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation of a
document written in HTML.
The reason that they are called cascading is that the styling or formatting can be applied at many different points during the life of the webpage but unless the style is modified or overwritten, the original styling stays in effect.
CSS is designed so that the person authoring a web page can separate the content from the presentation.
This includes aspects such as the layout, colours, and fonts.
Separating the two aspects can has the following benefits:
Some of the most important CSS3 features are:
Do not put styling instructions in the HTML file. Always use an attached style sheet.
The reasons for this are:
Click here to find out how to attach a style sheet