I am looking to format the code below to resemble the layout shown in the image using Bootstrap 3.3. When there isn't enough space to show all elements in a single line, I want them to stack vertically so that each element utilizes the entire width of the screen.
Additionally, my combo-boxes may change in size and I would like to apply Bootstrap's rounded corners to all corners of these elements.
<div>
<select>
<option>Opt1</option>
<option>Opt2</option>
</select>
<select>
<option>Opt1</option>
<option>Opt2</option>
</select>
<button>Button</button>
</div>