Full Width Split Dropdown Button in Twitter Bootstrap

Question

I have a place on my site which is using a bunch of button elements styled with btn-block (example from the Twitter Bootstrap Docs). I now want to switch some of them to split buttons (example), but I can't seem to get the split buttons and the normal buttons to be the same length.

I have experimented with all kinds of things, but I can't seem to find a way to do this. Has anyone ever managed to do it? Keep in mind that I do not want to hard-code the width of any elements if I don't have to. (Note that this includes not using hard-coded percentages either.) If it is absolutely necessary, I am OK with defining a width for the toggle part of the button (because I know there will only be a single arrow character in there) but want to specify as few "magic numbers" as possible in order to keep the code maintainable in the future.

Answer 1

Wrap the dropdown-lead in a container:

(Note: This example is for Bootstrap 2.x)

.dropdown-lead {
  width: 100%;
}

.leadcontainer {
  left: 0;
  position: absolute;
  right: 30px;
}

.dropdown-toggle {
  width: 30px;
  float: right;
  box-sizing: border-box;
}

.fillsplit {
  position: relative;
}

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/2.3.2/css/bootstrap.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/2.3.2/js/bootstrap.min.js"></script>

<button class="btn btn-block btn-primary" type="button">Block level button</button>
<div class="btn-group btn-block fillsplit">
  <div class="leadcontainer">
    <a class="btn btn-primary dropdown-lead" href="#"><i class="icon-user icon-white"></i> User</a>
  </div>
  <a class="btn btn-primary dropdown-toggle" data-toggle="dropdown" href="#"><span class="caret"></span></a>
  <ul class="dropdown-menu">
    <li><a href="#"><i class="icon-pencil"></i> Edit</a>
    </li>
    <li><a href="#"><i class="icon-trash"></i> Delete</a>
    </li>
    <li><a href="#"><i class="icon-ban-circle"></i> Ban</a>
    </li>
    <li class="divider"></li>
    <li><a href="#"><i class="i"></i> Make admin</a>
    </li>
  </ul>
  <div>
  </div>

Answer 2

I was looking for the same kind of behavior and found this flexbox solution: http://codepen.io/ibanez182/pen/MwZwJp

It's an elegant implementation which makes use of the flex-grow property.

Just add the .btn-flex class to the .btn-group in your HTML. This is all the CSS you need:

.btn-flex {
    display: flex;
    align-items: stretch;
    align-content: stretch;
}

.btn-flex .btn:first-child {
    flex-grow: 1;
}

Credit goes to the author of the pen: Nicola Pressi

Answer 3

If you add the class btn-block to the .btn-group element and give the dropdownbutton elements % widths, that'd do the trick.

.dropdown-lead{
    width: 96%;
    box-sizing: border-box;
}
.dropdown-toggle{
    width: 4%;
    box-sizing: border-box;
}

Here's an example: http://jsfiddle.net/eBJGW/5/