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

Code Example 1

'em' units for the font-size property will be relative to the'font-size of the parent element'.
'em' units on other properties other than font-size will be relative to the
font-size of the current element. 'rem' units sizes will always be relative 
to the font-size of the root html element.

Code Example 2

/*realative to the font-size*/

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