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

Code Example 1

.element {
    /* https://developer.mozilla.org/en-US/docs/Web/CSS/box-shadow  */
  
 	/* offset-x | offset-y | blur-radius | spread-radius | color */
 	-webkit-box-shadow: 0px -1px 30px -2px rgba(0,0,0,0.75);
	-moz-box-shadow: 0px -1px 30px -2px rgba(0,0,0,0.75);
	box-shadow: 0px -1px 30px -2px rgba(0,0,0,0.75); 
}

Code Example 2

#example1 {
  box-shadow: 10px 10px 8px #888888;
}

Code Example 3

box-shadow: 3px 3px 6px 5px #ccc;

or

box-shadow: 0px 5px 17px -7px rgba(0, 0, 0, 0.75);

Code Example 4

/* Keyword values */
box-shadow: none;

/* offset-x | offset-y | color */
box-shadow: 60px -16px teal;

/* offset-x | offset-y | blur-radius | color */
box-shadow: 10px 5px 5px black;

/* offset-x | offset-y | blur-radius | spread-radius | color */
box-shadow: 2px 2px 2px 1px rgba(0, 0, 0, 0.2);

/* inset | offset-x | offset-y | color */
box-shadow: inset 5em 1em gold;

/* Any number of shadows, separated by commas */
box-shadow: 3px 3px red, -1em 0 0.4em olive;

/* Global keywords */
box-shadow: inherit;
box-shadow: initial;
box-shadow: unset;

Code Example 5

.yourElement {
  /* offset-x | offset-y | blur-radius | spread-radius | color */
  -webkit-box-shadow: -2px -1px 15px 7px rgba(0,0,0,0.5);
  -moz-box-shadow: -3px -2px 30px 14px rgba(0,0,0,0.425);
  box-shadow: -4px -3px 45px 21px rgba(0,0,0,0.35);
}

Code Example 6

#Box-shadow-example {
Box-shadow:0 10px 20px rgba(0,0,0,0.19), 0 6px 6px rgba(0,0,0,0.23);
}
<!-- offset-x, offset-y, (blur-radius and/or spread-radius=optional) and color-->

Learn ReactJs, React Native from akashmittal.com