Theme development

I tried to reach out to the developer of the Twentyfifteen theme, without success.
https://www.drupal.org/project/twentyfifteen

I am trying to remove the margins/padding for the main image in both node and teaser views, but the whole content section is inside a div with margins. I want the image to fill the entire box. (See attached image. This is what I'm trying to achieve.) I can't seem to find a way to, via css, tell the image, "reach out of the current div and fill the grandparent's div."

Hi, try to crate Twig Template for my custom Block, but it not working(

Twig Template naming conventions said:
For example, "block--block--1.html.twig" would be used for the first user-submitted block added from the block administration screen since it was created by the block module with the id of 1.

..but it not working..

How do I make my header disappear and make my nav move up and become fixed

here is my website nextspecs.com

here is the website I want my header and navigation to mimic lifeinthegrid.com

I have a theme A and then themes B and C that are base on theme A.

When I have build my site with theme B I have blocks like contact and when I changed the theme from B to C the machine name of that block became c_contact. That of course ruined my theme. (b_contact never existed)

A) Is this the action Drupal should do?

B) Is there a way to disable this kind of behaviour?

C) How should I work with this?

I am building a website where i generate a submenu based on my main navigation.
The structure looks like this:

• Home
• About
• Work at
• vacancies
• contact

when u land on 1 of the level 1 pages, a submenu will appear in the sidebar with the children links of this page.
i want the parent title to show above this menu.

also, on the vacancies page theres a overview of vacancies, and when you go to one of the detailed vacancies i want it to show
"Work at" and not "vacancies" in the submenu title.

Hi... I need a help with Drupal 8 templates, please.

I created a custom block, I can create a theme for the custom block (the instance), but I can't create a theme for the Custom Block TYPE (let's call it "the prototype").

I meant, is there a way to theming the different Custom Block Types?

And a "bonus question": Why in the Theme Debug I can see "block--block-content.html.twig" twice? Should I see one "block--block-content.html.twig" and one "block--CUSTOM-BLOCK-TYPE-content.html.twig"