Websites with continuous background

You can create a div in your html that contains the objects to which you are going to put background

<div class="fondo">
     <!-- Código html -->
</div>

Then, you must create the image in SVG (Scalable Vector Graphics) format, save it in a folder of your project (your_project / images / background.svg) and then invoke it from bootstrap.css or from your file CSS like this:

.fondo {
    background: url(../images/background.svg) top no-repeat;
    background-size: cover;
}