[UIK-2371][wizard] update styles

[ilyabrower]

Motivation and Context

We had some strange paddings for Stepper.

• Fixed styles for Stepper and Sidebar.
• Updated illustrations for documentation.
• Updated example with custom stepper.

How has this been tested?

Manually using storybbok and our documentation.

Types of changes

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).
• Nice improve.

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly or it's not required.
• Unit tests are not broken.
• I have added changelog note to corresponding CHANGELOG.md file with planned publish date.
• I have added new unit tests on added of fixed functionality.