Full width search

example.html

<style>
.container {
  display: table;
  position: relative;
  width: 100%;
}

button,
.input {
  display: table-cell;
  vertical-align: top;
}

input,
.input {
  width: 100%;
}

button {
  float: right;
}
</style>

<div class="container">
  <div class="input">
    <input type="text" />
  </div>
  <button>Search</div>
</div>