difference between content box and border box code example

Example 1: stop padding from changing div size

-webkit-box-sizing: border-box; /* Safari/Chrome, other WebKit */
-moz-box-sizing: border-box;    /* Firefox, other Gecko */
box-sizing: border-box;         /* Opera/IE 8+ */

Example 2: difference bw box and border box

.alligator-box {
  box-sizing: border-box;
  width: 125px;
  height: 125px;
  border-width: 10px;
  padding: 40px;
}

Example 3: difference bw box and border box

.alligator-box {
  box-sizing: content-box;
  width: 125px;
  height: 125px;
  border-width: 10px;
  padding: 40px;
}