Benefits of Cascading Style Sheet

CSS is flexible

Styles can be written in one place as separate style sheets file. And we can assigned to HTML elements through class or ID properties. It's way easier and quicker to change styles across a whole site when they're defined in one separate file.

CSS is Lightweight

When Using CSS (like class="main-nav") creates far smaller HTML files than writing style into every HTML tags (like border="1" cellpadding="3" cellspacing="1" backgroundcolor="#ffc").

CSS helps separate style from content

Keeping your style definitions separate from your content and content-structure makes it possible to reuse the same content for different media. This includes styling pages differently for printing, as well as other user agents like voice and mobile devices.