Check out example codes for "how to style scrollbar in div". It will help you in understanding the concepts better.

Code Example 1

#style-1::-webkit-scrollbar-track
{
	-webkit-box-shadow: inset 0 0 6px rgba(0,0,0,0.3);
	border-radius: 10px;
	background-color: #F5F5F5;
}

#style-1::-webkit-scrollbar
{
	width: 12px;
	background-color: #F5F5F5;
}

#style-1::-webkit-scrollbar-thumb
{
	border-radius: 10px;
	-webkit-box-shadow: inset 0 0 6px rgba(0,0,0,.3);
	background-color: #555;
}

Code Example 2

::-webkit-scrollbar {
    width: 12px;
}
 
::-webkit-scrollbar-track {
    -webkit-box-shadow: inset 0 0 6px rgba(0,0,0,0.3); 
    border-radius: 10px;
}
 
::-webkit-scrollbar-thumb {
    border-radius: 10px;
    -webkit-box-shadow: inset 0 0 6px rgba(0,0,0,0.5); 
}

Code Example 3

/* width */
*::-webkit-scrollbar {
  width: 10px;
}

/* Track */
*::-webkit-scrollbar-track {
  background: #f1f1f1; 
}
 
/* Handle */
*::-webkit-scrollbar-thumb {
  background: #888; 
}

/* Handle on hover */
*::-webkit-scrollbar-thumb:hover {
  background: #555; 
}

Learn ReactJs, React Native from akashmittal.com