why put # in elements in css code example

Example 1: css how to style a div

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

Example 2: how to edit divs in css

# or . depends on class or id