Theme development

hello I am theming html5 theme to Drupal 8 please help http://morella.e-tck.com multilevel menu to be active

the original theme is here http://krasotaiskusstva.com/ki/?theme=morellahtml

Hello,
I am trying to do some theming for Drupal 8 and was trying to understand what would be the best way to understand what theme is being used on any given page. I remember using theme developer module in D7 and later doing dpm of the page array after theme developer started having issues.

1. Is there any helper module for D8, if so where can I learn to use them?
2. If there are no contrib modules, what other options do I have?

I am trying to develop an amazing theme and the theme has it's background image in CSS not in the Html code, I would like to know if and how could I get a node field image url to become available in the CSS code. The theme will be converted from The Big Picture bootstrap theme and it's code is a little weird for me.

Dear everyone,

I have a title field in Views on which "link to content" is enabled, but now the title style is taking the default theme style for all links. I did append a div tag on the .tpl file but that didn't work. When I check the link in inspector it shows like this:

If a content type had several images, how can we display the 1st image from field_image in a theme twig?

My theme has styling for custom content type Article Teaser image (field_image) and I want to apply this styling to another content type (Review) teaser which uses a different image type (field_intro_image). I've copied the node--article--teaser.html.twig to node--reviews--teaser.html.twig which has {{content|without('field_image', 'links')}} within.

But the teaser image does not get displayed correctly. I've also tried {{content|without('field_intro_image', 'links')}}, how do I correctly do this?