[Customizr] Full width colored div

Hi,
how can I, in a page, have a full-width div ?

I’ve tried something like :

#my-full-width-div{
  width: 100%;
  float: left;
  padding: 20px;
  background: #2680BE;
  position: relative;
}

with

<div id="my-full-width-div"> Some text </div>

but there is still a space on the left. I think it comes from a kind of wrapper, any idea to solve that in the simplest way ?

Thanks