<div>
  <p>Перелік</p>
    <ul>
      <li>Пункт 1</li>
      <li>Пункт 2</li>
      <li>Пункт 3</li>
    </ul>
  <label for="select">Задати колір нижнього кордону: </label>
<select class="input" id="select">
  <option value="currentColor" name="color" selected>currentColor</option>
  <option value="coral" name="color">coral</option>
  <option value="cyan" name="color">cyan</option>
</select> 
</div>
body {
    color: blue;
}
div {
    padding: 30px;
    width: 300px;
    height: 300px;
    border: 5px solid;  
}
p {
    font-size: 30px;
    width: 80%;
}
li {
    margin: 10px;
    padding: 10px 0;
    color: green;
    display: inline-block;
    position: relative;
    border-bottom: 3px solid currentColor;
}
li:hover{
  color: red;
}
ul{
  list-style: none;
}
.input{
  font-size: 16px;
}
label{
  display: inline-block;
  margin-bottom: 10px;
}
$('#select').on('change', function() {
  var color = $(this).find(":selected").val();
  $('li').css( 'border-color', color );
});

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js