Resolve styling mismatches in the SearchField button

[PKulkoRaccoonGang]

Description

The button in the SearchField component has a few styling issues that should be addressed:

1. When focused, the button shows a rounded outline even though the button itself has square corners.
2. The text inside the button ("search") starts with a lowercase letter, but it should begin with an uppercase one.
3. When the button is focused via keyboard navigation, unexpected black inner borders appear.

SearchField external button

Paragon Button component