CSS inline-block white space [on hold]

I need to render white space in inline-block but instead of white space, I will not render anything. I can not figure out where the CSS'm wrong.

CSS:

.foo {
    display:inline-block;
}

HTML:

<span class="foo">a</span><span class="foo"> </span><span>class="foo">b</span>

`http://ift.tt/1IdOUel