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

Code Example 1

p:first-child {
  font-size: 1.5em;
}

Code Example 2

:first-of-type {
	//styles here
}

:first-child {
	//styles here
}

:nth-child(1) { //the benefit of this is you can do it for 2nd, 3rd etc...
	//styles here 
}

Code Example 3

:first-child {
	//styles here
}

:nth-child(1) { //the benefit of this is you can do it for 2nd, 3rd etc...
	//styles here 
}

Code Example 4

#content div:first-child {
/*css*/
}

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