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

Code Example 1

-webkit-border-radius: 5px;
-moz-border-radius: 5px;
border-radius: 5px;

Code Example 2

#roundCornerID {
    border-radius: 30%;
    width: 200px;
    height: 150px;   
}

Code Example 3

#rcorners {
  border-radius: 25px;
}

Code Example 4

.abcclass {
  border-radius: 0px;  // for no radius
  
}

Code Example 5

/* Set rounded corners with border-radius property */

.class {
  border-radius: 4px;
}

.circle {
  border-radius: 50%;
}

Learn ReactJs, React Native from akashmittal.com