Hi! Stepping in for Max today to answer this one 
First, I’m glad that the solution worked for you! You can definitely use this CSS code to modify any Comments widget 
As for the other apps, the codes for changing the width may be slightly different. You can try and search for the width setting first, and if it’s not there, we’ll be happy to assist you with the new CSS.
Speaking of the separate Comments section under each Blog post, unfortunately, it’s not possible to achieve as of now due to the technical peculiarities of both apps. However, I totally see the vision – it would be great to implement such a functionality in the future 
Here’s a Wishlist topic that sounds like what you have in mind: Ability for visitors to leave a comment. Leave a vote here to be notified of any changes. Stay tuned!