add boreder bottom code example

Example 1: css border bottom

.bottomBorder {
  /*           width style color  */
  border-bottom: 5px solid black;
}

Example 2: css border botttom

div {
  border-bottom: 4px dashed blue;
  background-color: gold;
  height: 100px;
  width: 100px;
  font-weight: bold;
  text-align: center;
}