[research]: refactor and cleanup styles

[wainola]

There is a lot of CSS in explorer that is mostly tied to old implementation when this was part of transfer UI mono repo. Also, we are using mui as dependency, for which we are mostly using simpler components like container or typography, not leveraging the full potential of this dependecy.

Two main goals:

• check cleanup of the theme and overall styles
• explore removal of mui as dependency taking into account next features. Explore usage CSS modules or more native approach
• remove some of the inline styles that are present in some small markup

Implementation details

Testing details

• Explorer UI should retain current looks

Acceptance Criteria

• clean up of the CSS
• if applicable, removal of mui dependency.