How To Restrict Width of Bootstrap 3 Dropdown-Menu in Navbar

Question

I would like to prevent the Bootstrap .dropdown-menu from ever being wider than the main nav bar (which I have restricted to be the width of the .container class). I'd like for the dropdown menu to take up the width of the container class, but it shouldn't extend beyond that on either side.

Any ideas how to accomplish this, preferably using CSS?

Here's an example of what it currently looks like and what I'd like it to look like:

Here's a boiler plate navbar with a dropdown menu that has one really long menu item:

<link rel="stylesheet" type="text/css" href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<script type="text/javascript" src="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js"></script>

<div class="container">
  <nav class="navbar navbar-default" role="navigation">
    <!-- Brand and toggle get grouped for better mobile display -->
    <div class="navbar-header">
      <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1">
        <span class="sr-only">Toggle navigation</span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
      </button>
      <a class="navbar-brand" href="#">Brand</a>
    </div>

    <!-- Collect the nav links, forms, and other content for toggling -->
    <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
      <ul class="nav navbar-nav">
        <li class="active"><a href="#">Link</a></li>
        <li><a href="#">Link</a></li>
        <li class="dropdown">
          <a href="#" class="dropdown-toggle" data-toggle="dropdown">Dropdown <span class="caret"></span></a>
          <ul class="dropdown-menu" role="menu">
            <li><a href="#">Action</a></li>
            <li><a href="#">Another action a really long menu item that extends way beyond the limits of "container" and may even extend beyond the view port area to the right, making some of the text unreadable.</a></li>
            <li><a href="#">Something else here</a></li>
            <li class="divider"></li>
            <li><a href="#">Separated link</a></li>
            <li class="divider"></li>
            <li><a href="#">One more separated link</a></li>
          </ul>
        </li>
      </ul>
    </div><!-- /.navbar-collapse -->
  </nav>
</div>

Answer 1

Explanation

Bootstrap's adds position: absolute to the .dropdown-menu class. As you may know, all absolutely positioned elements are positioned in relation to the first parent element they find with position: relative. In Bootstrap, this is provided by the .dropdown wrapper

So if you want to position the element relative to the container, and not the nav item, we'll have to remove relative positioning from the .dropdown wrapper. You can do this by resetting the value to the initial value for the position property, which is static.

Congratulations! The menu is no longer constrained by the .dropdown element, but we still have some work to do.

Because bootstrap was not intending to space constrain the menu, menu items are given the property white-space: nowrap so they'll extend as long as they need. Think lines of code inside code blocks here on stack overflow (1 line = 1 line). Since we want the line to eventually end, this won't do. So we'll reset the anchor tags back to white-space: normal.

At this point the .dropdown-menu should take up the full size of the .navbar (which itself takes up the full size of the .container). This is where yamm3 is doing something really cool. It sets left: auto on the dropdown-menu.

According to MDN on the left property:

auto is a keyword that represents:
for absolutely positioned elements, the position of the element based on the right property and treat width: auto as a width based on the content.

So setting the .dropdown-menu to left:auto will cause the menu to start in its current location and extend all the way to the right of the container.

Just Codes

Just add the .fill-width class to your .dropdown element and include the following CSS:

.fill-width.dropdown {
    position: static;
}
.fill-width.dropdown > .dropdown-menu {
    left: auto;
}
.fill-width.dropdown > .dropdown-menu > li > a {
   white-space: normal; 
}

Working Demo in jsFiddle

.full-width.dropdown {
    position: static;
}
.full-width.dropdown > .dropdown-menu {
    right: 0;
}
.full-width.dropdown > .dropdown-menu > li > a {
   white-space: normal; 
}


.fill-width.dropdown {
    position: static;
}
.fill-width.dropdown > .dropdown-menu {
    left: auto;
}
.fill-width.dropdown > .dropdown-menu > li > a {
   white-space: normal; 
}

<link rel="stylesheet" type="text/css" href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<script type="text/javascript" src="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js"></script>


<div class="container">
    <div class="navbar navbar-inverse">

        <!-- Header -->
        <div class="navbar-header">
            <button type="button" class="navbar-toggle" 
                    data-toggle="collapse" 
                    data-target=".navbar-collapse">
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
            </button>
            <a class="navbar-brand" href="#">
                Bootstrap 3 Skeleton
            </a>
        </div>
        <!-- Navbar Links -->
        <div class="collapse navbar-collapse">
            <ul class="nav navbar-nav">
                <li class="dropdown">
                    <a href="#" class="dropdown-toggle" 
                    data-toggle="dropdown">
                        Normal <span class="caret"></span>
                    </a>
                    <ul class="dropdown-menu" role="menu">
                        <li><a href="#">Action</a></li>
                        <li><a href="#">Another action</a></li>
                        <li><a href="#">Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Long
                            </a></li>
                        <li class="divider"></li>
                        <li><a href="#">Separated link</a></li>
                        <li class="divider"></li>
                        <li><a href="#">One more separated link</a></li>
                    </ul>
                </li>   
                <li class="dropdown full-width">
                    <a href="#" class="dropdown-toggle" 
                    data-toggle="dropdown">
                        Full Width <span class="caret"></span>
                    </a>
                    <ul class="dropdown-menu" role="menu">
                        <li><a href="#">Action</a></li>
                        <li><a href="#">Another action</a></li>
                        <li><a href="#">Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Long
                            </a></li>
                        <li class="divider"></li>
                        <li><a href="#">Separated link</a></li>
                        <li class="divider"></li>
                        <li><a href="#">One more separated link</a></li>
                    </ul>
                </li>          
                <li class="dropdown fill-width">
                    <a href="#" class="dropdown-toggle" 
                    data-toggle="dropdown">
                        Fill Width <span class="caret"></span>
                    </a>
                    <ul class="dropdown-menu" role="menu">
                        <li><a href="#">Action</a></li>
                        <li><a href="#">Another action</a></li>
                        <li><a href="#">Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Really Long
                            </a></li>
                        <li class="divider"></li>
                        <li><a href="#">Separated link</a></li>
                        <li class="divider"></li>
                        <li><a href="#">One more separated link</a></li>
                    </ul>
                </li>   
            </ul>
        </div>
    </div>
</div>