Minor visual design bugs, do not require additional design assets

Steps to reproduce

1. Go to create a new Wikipedia account
2. Enter a valid new account name and password and tap to proceed to the the CAPTCHA screen

Expected

• The introductory text "To help protect..." should use the Material Subhead text style
• "Tap CAPTCHA to reload text" should be centered-aligned under the CAPTCHA image
• Width of text, input fields, and buttons should be the same

Actual

- CAPTCHA content is on a pale gray background over a white background.

• Introductory text is larger than expected
• Reload text is left aligned
• Text, inputs and button paddings differ