Module development and code questions

Hi everyone,
I made a view with views data export contrib module, thants to I download a CSV file of some information. Well, I need to download this file, and save it into drupal filesystem, in particular into public file, or attach it to an email, for example. How can I do this?

Can I make this with Drupal controller?

Rendering a block using twig teak via twig template gives error:

This block is broken or missing. You may be missing content or you might need to enable the original module

Any suggestions to fix this error?

Tried to fix using 

https://www.drupal.org/project/recreate_block_content

But the issue is not fixed.

Requirements

Add a video library related to the chapters in a book and play them in the site

Steps followed

1. Using the book module created a hierarchy of the chapters in a node

2. Created a video content type and configured in the book module for the parent and childs

3. Created a view as a block and with the contextual filters and relationship displayed the list

Issues

1.

Unable to render the view via twig teak module (drupal_view) and related twig template 

Hello All,

I'm very new in Drupal 8 development, I have created a basic webform and now i want to add custom css to make it more attractive so how can i add? Any lead will be appreciated..

We have a node type called: MEETING On Meeting we have a user entity reference called: PARTICIPANTS I create several MEETING's and reference 2 users: USER1 AND USER2

Now I want to build a dynamic view we can use URL arguments in contextual filters to show all meetings with USER1 and USER2

I create a view called VIEWMEETINGS I set PARTICIPANTS field as the contextual filter and check "Allow multiple values"

view path settings are MYSITE/VIEWPARTICIPANTS/%

I am using Drupal Commerce and looking for a way to exempt some items from general tax.

I have tried a couple of modules to achieve this for instance Commerce Product Tax, Commerce Product Tax Conditions but they don't seems to be giving an option of selecting which items are tax free.

At product creation level I am expecting an option to select which items are tax exempt.