Update styles.css path with new branding effort

[Yoshani]

Purpose

With the new branding effort, the path of styles.css file which can be defined to override styles should be changed.

Related Issues

• Issue Integrate Branding capabilities to the Authentication, Recovery & My Account portals using file_based approach. product-is#15729

Related PRs

• PR File based UI branding support #3931
• PR Add layout-resolving logic #3943
• PR Change layout resolving logic #3951

Checklist

• e2e cypress tests locally verified.
• Manual test round performed and verified.
• UX/UI review done on the final implementation.
• Documentation provided. (Add links if there are any)
• Unit tests provided. (Add links if there are any)
• Integration tests provided. (Add links if there are any)

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines?
• Ran FindSecurityBugs plugin and verified report?
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets?