Server error occurred while processing request

Hello Awesome people! I am new in Shopware development. After studying last few days, I have learned how to develop Shopware theme, not fully but a bit.

 

I followed a tutorial to develop my own theme header. But While I am going to activate the theme, I am getting this error:

A server error occurred while processing your request for shop „Demoshop“: File _modules / main-navigation.less not found. in all.less

I have to mention that I already created that main-navigation file into modules folder under less. And at the front end my site is look like this:

Image URL: Dropbox - File Deleted

It will be great if anyone can guide me. Also Please share some shopware theme development resources, which are easy to udnerstand and follow.

 

Thanks