I'm trying to implement the following HTML structure using HTML5 and CSS. The section elements have to be next to each other. The right section element must have a margin-left of 30 px and a fixed width of 220 px.

What I have so far is as follows:
HTML
<section id="section-left">My left section</section>
<section id="section-right">My right section</section>
CSS
#section-left {
float: left;
}
#section-right {
float: right;
width: 220px;
margin-left: 30px
}
My problem is that the left section does not fill the remaining space up to the right section element. My result looks as follows:

What is the problem here?