Theme development

Hello :)

How to add a class on all form in my theme. 

I want to add on all input type text a class for exemple form-input-text.

I have to rebrand and custom design the theme of a live and running Drupal 8 website. I wondered if there is any best practices post or blog that anybody could share or anybody would want to share their practices for such similar case.

I wanted to create a new sub theme on a suitable base theme.

In my limited experience I imagine if I want to design and test it in my localhost then I have to create a copy of the website in my localhost and then i would have to reinstall the website again on the live server.

For a small project, I'm working on a particularly not resource-efficient hosting, and I'd like to create a grid-organized home page layout (similar to the example in the image) without use of Views. I'm doing a lot of research, but I only find modules that partially solve the problem.
Can someone recommend something that can bring me closer to this result?
If not, I will be forced to use Views

I am new to Drupal and I  am having hard time in learning it.

I created a custom content type named movies. It has following fields

1. title
2. Poster
3. Description
4. Release year

Then I  added the content using devel module. I created a view for this content to display the recently added 5 movies and added block display. All I want is to theme this block.

I tried using template block--views-block--test-block-1.html.twig but I am unable to access content fields. Can anyone help me in this issue?

Could anyone  tell me the detail about solution for the above topic? Thanks very much

Here is the menu.twig.html template provided by Drupal Bootstrap :