How To Round Edges Of Featured Collection?

[RMTPerformance]

Hi, I want to know how to round the edges of my featured collection just like the image below.

I want to round the edges of the collection itself. Not the products within the collection.
As a side-note I would need to adjust the width of the featured collection so the rounded edges are visible.

If anyone could help with this query I would be grateful. Thank-you for your time in advance.
Source - https://autoid.co/
Our page - https://rmtperformance.com/

(Source)

(Our page)

[RMTPerformance]

This should work however when applied I cannot see the edges due to the collection being so wide, is there a way to edit the width of the collection similar to the source I posted above so I can actually see the rounded edges if that makes sense?

As you can see I cannot see the edges.

[RMTPerformance]

Unfortuantley this did not work, I cannot see the edges because of how wide the collection is, any idea on how I reduce the width of the collection?