how to increase bottom border for navigation bar in bootstrap with CSS

basically, i want to add colored border below navigation bar (default fixed navbar) in bootstrap. For that i have added border style in CSS and it's working which shows border below navigation bar but i want this border somewhat thicker and i am not getting how to do this? Code-

<div class="tab-content">
  <div id="home" class="tab-pane fade in active">
    <h3>HOME</h3>
    <p>home</p>
  </div>
  <div id="menu1" class="tab-pane fade">
    <h3>Menu 1</h3>
    <p>home1</p>
  </div>
  <div id="menu2" class="tab-pane fade">
    <h3>Menu 2</h3>
    <p>home2</p>
  </div>
  <div id="menu3" class="tab-pane fade">
    <h3>Menu 3</h3>
    <p>home3</p>
  </div>
 </div>
</div>
</body>
</html>

and CSS as below

.navbar-default{
background-color: #A52A2A !important;
border-style: solid;
border-bottom-width: 15px;
border-bottom-color: #7FFF00 !important;
}

but here this border-bottom-width: 15px; property not going to work.... so is there any option to increase thickness of border? if u have any other solution then also suggest me....thank u