If mark-up is basic descriptive language, style sheet languages like CSS (Cascading Style Sheets) are the sensory language that gives life to that description. As such, it is an add-on type of language, that expands the description of a given element.

 

Mark up is like a noun, which literally states what something is. For instance, I can point to an object and state that it is a car. In doing so, I have described what it is, and (if you’ll allow me to extend the metaphor) “marked it up”.

Styles, however, are more like adjectives, which add extra values or properties to the noun. Now, if I point to the same object and state that it is a large, red car, the basic understanding of what the object is doesn’t change – it is still a car. However, we also have additional descriptive information that tells us that it is large and red.

 

Without the nouns, the paragraph becomes completely non-nonsensical and looses all meaning, and the adjectives have absolutely nothing to work on. The same concept applies to HTML and CSS. While HTML can exist without CSS and still make sense, CSS without HTML is like throwing a bunch of adjectives onto a page without a single noun to give them context.