Web-designers use CSS or Cascading Style Sheets for separating page content like paragraphs or images from the stylistic elements of the page. These stylistic elements may comprise of colour, fonts, layout etc.
The term generally used for this is ‘Separation of Content from presentation.’
CSS represents a breakthrough in web designing as it equips web developers with the ability to control styling and layout of multiple pages all at once. Web designers can choose a style for every HTML element and apply it to multiple web pages at per their requirement. To effect changes globally, the style needs to automatically update all elements in the web.
However, many people refrain from using CSS just because they lack a proper understanding of it. It nevertheless is worth investing time to learn CSS, as the advantages gained through its use are tremendous.