CSS: make drop-down menu as wide as top bar

I've made a top bar that contains drop-down MENU button on the right side. But this drop-down content has exactly the same size (width) as my MENU button. Finally - my goal is to make this drop-down content as wide as the top bar is.

My HTML code looks like this:

<div id="top-bar">
  <div class="dropdown">
    <button class="dropbtn">MENU</button>
    <div class="dropdown-content">
      <a href="#">Link</a>
      <a href="#">Link</a>
      <a href="#">Link</a>
    </div>
  </div>
</div>

And more important part - CSS:

#top-bar{
  left: 0;
  top: 0;
  float: left;
  width:100%;
  height:40px;
  background-color: black;
}
.dropbtn {
    background-color: blue;
    color: white;
    height: 40px;
    font-size: 12px;
    border: none;
    cursor: pointer;
}
.dropdown {
    float: right;
    position: relative;
    display: inline-block;
}
.dropdown-content {
    display: none;
    float: left;
    position: absolute;
    background-color: #f9f9f9;
    width: 100%;
    box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
}
.dropdown-content a {
    color: black;
    padding: 10px 14px;
    text-decoration: none;
    display: block;
}
.dropdown-content a:hover {background-color: #f1f1f1}
.dropdown:hover .dropdown-content {
    display: block;
    width: 100%;
    float: left;
    left: 0;
}
.dropdown:hover .dropbtn {
    background-color: blue;
}

If you want to see how does it look like HERE is jsFiddle link.
Don't you have any idea how to solve my problem?