Tiny gap under video HTML 5

It's because they are inline elements with resizable height (most inline elements are not explicitly resizable). If you set them to display: block; the gap goes away. You can also set vertical-align: top; to achieve the same result.

D8 How do I add a node ID as class to the <body> tag?

3
down vote
accepted
In mytheme.theme file: add the below code.

function mytheme_preprocess_html(&$variables) {
// Add node id to the body class.
$node = \Drupal::routeMatch()->getParameter('node');
if($node) {
$variables['attributes']['class'][] = 'node-' . $node->id();
}
}
This will add "node-{{nid}}" class in body tag.

The Simplest Way To Center Elements Vertically And Horizontally

The HTML

The idea, of course, revolves around flexbox. First, we create a container in which we want everything to be centered:

You can place this container div anywhere you want. In the live example above we've made it take up the whole width and height of the page.
The CSS

As we said earlier, we will be using only three lines of code. Here they are:

.container{
display: flex;
justify-content: center;
align-items: center;
}

Theme suggestion for D8 blocks

/**
* Implements hook_theme_suggestions_HOOK_alter() for form templates.
* @param array $suggestions
* @param array $variables
*/
function THEMENAME_theme_suggestions_block_alter(array &$suggestions, array $variables) {
// Block suggestions for custom block bundles.
if (isset($variables['elements']['content']['#block_content'])) {
array_splice($suggestions, 1, 0, 'block__bundle__' . $variables['elements']['content']['#block_content']->bundle());
}
}

Node type twig

You should be able to get the human-readable name of the content type (or the "label") by doing {{ node.type.entity.label }} in your node Twig template.

Twig taxonomy term entity reference ID

0
down vote
I figured it out, I was able to print the term ID of the category field using:

{{ node.field_category.entity.tid.value }} as I realised I was looking in the wrong direction. Drupal 8 use entity reference only so I needed to call the TID from the referenced entity which of course is a taxonomy term in my category field.