You don’t want to float each of them left, only the first one, and then make the second one display in block mode:
<li>
<span style="float:left; background-color:red">a</span>
<span style="display: block; background-color:green">b</span>
</li>You don’t want to float each of them left, only the first one, and then make the second one display in block mode:
<li>
<span style="float:left; background-color:red">a</span>
<span style="display: block; background-color:green">b</span>
</li>