When building a complex page, at some point you will be faced with the need to combine PHP and HTML to achieve your needed results. At first point, this can seem complicated, since PHP and HTML are two separate languages, but this is not the case. PHP is designed to interact with HTML and PHP scripts can be included in an HTML page without a problem.
Cascading Style Sheets tell browsers how to display HTML tags. These style rules override the default display rules that browsers have for HTML tags. The style sheets are cascading in that there can be a number of conflicting rules that can be applied to a particular tag but the most specifically targeted rules will override less specifically targeted rules.