beta.blog

Result:

HTML Code

<div id="container">
    <div id="divB">divB</div>
    <div id="divA">
      <input type="text" style="width: 100%" placeholder="this is the default text of this textbox" />
    </div>
</div>

CSS Code

#divB
{
  border:1px solid red;
  float:right;
  width: 100px;
}
#divA
{
  border: 1px solid aqua;
  overflow: hidden;
  padding-right: .5em;
}