only bottom border css 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;
}

Example 3: half border bottom

div {
    width: 500px;
    height: 100px;
    position: relative;
    padding-top: 20px;
    margin-top: 50px;
}

div::before {
    content: '';
    display: block;
    position: absolute;
    top: 0;
    width: 50%;
    left: 25%;
    border-top: 1px solid red;
}