Theme development

Have fresh Drupal 8 install with Bootstrap 3 and sub-theme created as per: https://www.webwash.net/getting-started-bootstrap-drupal-8/

Have a couple articles listed in the homepage in <div class="views-row">. As per above tutorial, I'm taking variable from bootstrap/assets/stylesheets/bootstrap/_variables.scss and customizing them in scss/_default-variables.scss

Just trying to put a border on this class but having a hard time figuring out where exactly to do it.

I'm struggling to override the template on the admin interface for a content type. I'm going to need to do several modifications to the edit form to meet the editor's requirements, however, I seem to be unable to get this to override.

The page source gives me the following

http://gruplaela.uji.es/__D8/node/39

On this page I have a field called "Authored by" and the field type is Entity Reference. I'm trying to style it but I cant get it to sit inline like the other fields (which are field type Text). Rather the two field items sit on top of each other and push the following field to the right (as if it were float: left in CSS).

What I would like to have is something like this:

Authored by: Patricia Salazar Victòria Codina

In Drupal 7 I could create an external .php file and call it from inside a block by including the php file  

<?php
include_once("./".$theme_path ."/blocks/header_bar.php");
?

Is it possible to call an external twig file in Drupal 8 from a block? 

Thanks,

Nick

hi to everyone. I'm very new. I'm german and apologies my english :/.

I think this might be related to theme development. TPL files seem to be involved in any case (but I am not certain by a long shot—I don't even know what I don't know, and don't even know how to diagnose the issues I'm having). Anyway, here goes:

I'm having some strange issues with D7 (D8 ain't an option right now, for reasons too complicated to get into here), and some module interactions and the way things get displayed.