fix: initial loading spinner not centered (for suspense fallback)

[panteleymonchuk]

Description of change

Close #1452

Change position of spinner from top-left corner to center (for Suspense fallback)
It's a small update. We don't need opened issue for that.

Before

After

Change checklist

Add an x to the boxes that are relevant to your changes, and delete any items that are not.

• My code follows the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[begonaalvarezd]

base branch should be main not dev 🙏🏼