add scroll shadow on the right and left sides

[itisAliRH]

Related #14600: bthe ackdrop shadow in scroll list

https://user-images.githubusercontent.com/8046843/191488998-7f720a9d-f2c9-47aa-9b41-a3e0f5619d26.mp4

Known issue

Any background colour of elements is shown on top of these shadows

How to test the changes?

(Select all options that apply)

• [ ] I've included appropriate automated tests.
• [ ] This is a refactoring of components with existing test coverage.
• [ ] Instructions for manual testing are as follows: 1.

License

• [x] I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.