Check out example codes for "how to edit divs in css". It will help you in understanding the concepts better.

Code Example 1

# or . depends on class or id

Code Example 2

/*
<div class="#">
	<p>Hello World</p>
</div>
*/
/*put a dot in front of the name from your class*/
.#{
	display: block;
  	margin: auto;
  	width: 50%;
}

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