Check out example codes for "How to make a round corner in CSS". It will help you in understanding the concepts better.

Code Example 1

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

Code Example 2

#rcorners {
  border-radius: 25px;
}

Code Example 3

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

.class {
  border-radius: 4px;
}

.circle {
  border-radius: 50%;
}

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