border bottom 50% css code example

Example 1: css border bottom

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

Example 2: how to set border length in css without div

div {
  width   : 200px;
  height  : 50px;   
  position: relative;
  z-index : 1;
  background: #eee;
}

div:before {
  content : "";
  position: absolute;
  left    : 0;
  bottom  : 0;
  height  : 1px;
  width   : 50%;  /* or 100px */
  border-bottom:1px solid magenta;
}