inline block width

HTML

<div class="line">
<div class="second">
blablabla (width not known nor fixed)
</div>
<div class="first">
<span class="other">XXX</span>
<span class="item">Bla bla bla bla</span>
</div>
</div>

CSS

.second { float: right; }
.item { 
  display: inline-block;
  background-color: red;
  
}