I have a jumbotron from bootstrap and I want to darken its background without touching the text which is entered in it. Is there a way to do such a thing?

I have looked everywhere, but all solutions I've found darken the text as well.

What I have so far:

```css
.mainJumbotron {
    margin: 0px;
    height: 250px;
    text-align: center;
    background-image: url(http://i.imgur.com/qj2w73W.png);
    background-repeat: no-repeat;
    background-size: cover;
}
```

```html
<div class="jumbotron mainJumbotron">
    <h1 style="">Hakkımızda</h1>
</div>
```