Custom Background not Appearing

I have a very simple theme to which I need to add custom-background support.

When I go into appearance - customize, I am able to select a background image.

However, the background of the site never actually changes, and I can see that the output html contains

body class="home blog logged-in admin-bar no-customize-support custom-background"

But there are no style tags to be seen.

Does anyone have any suggestions as to what may be going wrong?

header.php

html
head
    titleTutorial theme/title
    link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet"
    link href="?php bloginfo('stylesheet_url'); ?" rel="stylesheet"
/head
body ?php body_class(''); ?
    div id="wrapper"
        div id="header"
        h1HEADER/h1
    /div

functions.php

?php
    $defaults = array(
        'default-image' = '',
        'default-preset' = 'default',
        'default-position-x' = 'left',
        'default-position-y' = 'top',
        'default-size' = 'auto',
        'default-repeat' = 'repeat',
        'default-attachment' = 'scroll',
        'default-color' = '',
        'wp-head-callback' = '_custom_background_cb',
        'admin-head-callback' = '',
        'admin-preview-callback' = '',
    );
    add_theme_support('custom-background', $defaults );
?

I also tried simply adding add_theme_support('custom-background'); but no luck.

I am using version 4.7.5