Check out example codes for "html overflow scroll only if needed with exemple". It will help you in understanding the concepts better.

Code Example 1

p {  
  width: 12em;
  height: 6em;
  border: dotted;
  /* le contenu n'est pas rogné */
  overflow: visible;  

Code Example 2

p {
  /* les ascenseurs sont toujours affichés */
  overflow: scroll;

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