how to do group selectors in css with class code example

Example 1: css how to style id

/*put a # infront of the id*/
/*<section id="example"></section>*/
#example{
	margin: auto;
}

Example 2: CSS how to select ID

#id-selector-name{
  font-size: 20px;
}

.class-selector-name{
  color: green;
}