Check out example codes for "what is css". It will help you in understanding the concepts better.

Code Example 1

What is CSS?
CSS stands for Cascading Style Sheets
CSS describes how HTML elements are to be displayed on screen, paper, or in other media
CSS saves a lot of work. It can control the layout of multiple web pages all at once
External stylesheets are stored in CSS files

Code Example 2

In this example all <p> elements will be center-aligned, with a red text color:

p {
  color: red;
  text-align: center;

Code Example 3

Is the standardised markup language (a subset of XML) that 
defines the layout of a webpage. 
HTML has no functional properties, other languages such as 
JavaScript must be used in order to manipulate the layout
and perform HTTP requests.
CSS (Cascading Style Sheets) is commonly used to style the
elements in the layout.

Code Example 4

Cascading Style Sheets
CSS is the acronym of “Cascading Style Sheets”. CSS is a computer language for laying out and structuring web pages (HTML or XML).*/

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