Add empty space between div's content and bottom border

Question

I am attempting to add a bottom border to a div for the purpose of a navigation bar. The effect I am trying to achieve:

Answer 1

As it currently stands you can't do this. You can't add a gap between an element and its own border. You can, however, add the border to its parent element (the div.item element in this case), then add padding-bottom to that same element to separate it from the a element:

$("a").click(function() {
  
  $(".current").removeClass("current");
  
  $(this).parent().addClass("current");
  
  });

.container {
}

.container .item {
  float: left;
  list-style-type: none;
  margin: 0 1px;
}

  .container .item a {
    color: black;
    text-decoration: none;
    background-color: green;
    width: 50px;
    font-size: 13px;
    text-align: center;
    font-weight: bold;
    display: table-cell;
    vertical-align: middle;
    height: 40px; 
  }

    .container .item.current {
      border-bottom: 2px solid red;  
      padding-bottom: 4px;
    }

  
  

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Note that I've also modified your JavaScript to add this .current class to the li element and not the clicked a element.