I'm new to javascript and I got no clue what's not working, i'm just trying to get the background of some h2 with the class "titre" to turn blue. For some reason, if it's a getElementById it works fine but if I use getElementsByClassName it doesn't work and I don't get suggestion after style.

I know I should just use CSS without js to do it but it's a school thing and I need to do it like that.
Thank you.

My js code:

```
function titre2(){
    var titreback = document.getElementsByClassName("titre");
    titreback.style.backgroundColor = "blue";
}

```

my HTML (where my class is):

```
<section>
        <article>
          <h2 class="titre" onblur="titre2();">Qu'est-ce que <em>Facebook</em> ?</h2>

```