WordPress admin bar bump for Bootstrap fixed navbar

functions.php

<?php

namespace MyTheme;

function setup() {
  add_theme_support('admin-bar', ['callback' => __NAMESPACE__ . '\\admin_bar_bump']);
}
add_action('after_setup_theme', __NAMESPACE__ . '\\setup');

/**
 * Admin Bar Bump
 * WordPress adds margin to the html element when the admin bar is showing.
 * We also need that margin on the navbar element, so we're tweaking
 * the default styling to add it.
 */
function admin_bar_bump() {
  ob_start();
  _admin_bar_bump_cb();
  $bump = ob_get_clean();
  echo str_replace('html {', 'html, .navbar.fixed-top {', $bump);
}