Input field should take the remaining width - css

Question

I am trying to build a form to add new users to some kind of entity. The idea is to have user avatars in a line and on the end of the line there is a input-field with a typeahead to insert new users.
I tried this some years ago and ended up using javascript as I was not able to do this in plain css (2).
The big question: is this somehow possible in css3?
Basic idea of code:
<div class="availableWidth">
<div class="list">
<ul>
<li><div class="avatar">...</div></li>
...
</ul>
</div>
<div class="form">
<div class="typeaheadField">
<input ...>
</div>
<button>+</button>
</div>
</div>
CSS:
.list ul li {
list-style-type:none;
display:inline-block;
}
button {
width:50px;
}
Basic Idea is that the box .availableWidth has some width (100%) the box .list grows in width (when new li items are added) as the box .form should shrink in width. Right to the input is a some pixels wide button. The input should take the remaining space.
Is that possible in css3 or will I need Javascript?

Answer 1

You can use flexbox, or you can use display table attributes in CSS. Take a look:
.container {
display: table;
width: 100%;
position:relative;
}
.avatar {
width: 50px;
height: 50px;
display: table-cell;
}
.input {
height: 50px;
display:table-cell;
vertical-align: middle;
}
.input input {
width: 100%;
box-sizing: border-box;
padding: 5px;
}
<div class="container">
<div class="avatar">
<img src="http://dummyimage.com/50x50/000/fff&text=Avatar"/>
</div>
<div class="avatar">
<img src="http://dummyimage.com/50x50/000/fff&text=Avatar"/>
</div>
<div class="avatar">
<img src="http://dummyimage.com/50x50/000/fff&text=Avatar"/>
</div>
<div class="input">
<input type="text"/>
</div>
</div>
<div class="container">
<div class="avatar">
<img src="http://dummyimage.com/50x50/000/fff&text=Avatar"/>
</div>
<div class="avatar">
<img src="http://dummyimage.com/50x50/000/fff&text=Avatar"/>
</div>
<div class="avatar">
<img src="http://dummyimage.com/50x50/000/fff&text=Avatar"/>
</div>
<div class="avatar">
<img src="http://dummyimage.com/50x50/000/fff&text=Avatar"/>
</div>
<div class="avatar">
<img src="http://dummyimage.com/50x50/000/fff&text=Avatar"/>
</div>
<div class="input">
<input type="text"/>
</div>
</div>
You can add all the avatars that you want at left side and the input rearrange automatically.

Answer 2

You want to make input 100% width relative to some container from avatars to button. You can get it by using table, flexboxes or formatting contexts and floats.
Here is last one http://jsfiddle.net/53f0yzeL/
Notice overflow:hidden rule for .avatars-wrapper, it make container to fit exactly between floated elements and .avatars side so you can make input 100% wide.