Theme development

I have written a custom theme preprocessor that returns the following error:

User error: "attributes" is an invalid render array key in Drupal\Core\Render\Element::children() (line 97 of core/lib/Drupal/Core/Render/Element.php)

I have looked at the documentation for the Drupal Element object, as well as the source code for the original method, and don't understand what is causing the error. Oddly, the elements render properly (including the attributes). Can anyone help me understand why this function seems to work, yet throws this error?

I'm using Drupal 8.31 and working on a Bootstrap subtheme, setting up my gulpfile.js in my subtheme to run tasks.

It looks like the csslintrc in the site root has some rules to lint for, and I was wondering if I should have a copy of this in my subtheme as well. If core is updated I'd have to have a copy to put back in my edits. Anyone know best practice for this?

Also, same question for eslintrc as well, what's best practice?

Thanks.

Rick

I am new to drupal. I needed help with making zen template a dropdown menu. I installed nice module and enabled it in the header but then when I click on existing links it does not dropdown .I know there might be file to modify it in the template folder but just don't know the name and how to do it.I needed someone to point me in the right direction.

Hello.

I´m new with Drupal, I can create a theme where the front use the effect parallax,how this example:

https://codepen.io/designbyremedy/full/aqjLx/
Example 2

I work alot with AngularJs and materializecss, but drupal confuse me a litlebit, if you can help me
I appreciate.

Thanks.

How to develop a drupal theme suitable for social networking like facebook?

Dear drupaler,
I've a problem that don't understand how solve, I've search it in all the web but really nothing to help me found,
I'll try to explain it.

PRE: I've a Mac and MAMP and Installed Druapl 8 via composer.