Hey man, glad you like things so far! Can help you out a bit for sure:

1. To get a nice background blur, you'll want to use a blur texture as a background image, then ensure its semi-transparent with opacity:

background-image:url($blurred-img);

Code example here: https://codepen.io/ariona/pen/geFIK

Typically for sidebars like the Groove app, I keep them at a fixed width, because if you think about it, what use does a responsive sidebar really have when something always looks good at one particular size?

Usually I shrink my main content, but keep something small like a sidebar static, then re-arrange things on mobile once I'm below 768 pixels.

Let me know if that helps!

helps big time!, the code example link is not working tho, am getting a 404 (Page Not Found)

Oh woops, I think I added a period by accident, try https://codepen.io/ariona/pen/geFIK