Validate Startup CSS

What does this MR do?

This MR fixes 2 Markup Issues which were discovered using https://validator.w3.org/.

1. Remove the type attribute from the startup css style tag since it is not needed (Warning Level) (reference)
2. Remove an invalid box-shadow value from the styles. This value was only representing an rgbavalue, which leds to an invalid style rule (reference). This box-shadow was never rendered since it is invalid therefore it can be removed safely, see Screenshots attached.

Screenshots (strongly suggested)

before	after

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• [-] Code review guidelines
• [-] Merge request performance guidelines
• [-] Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team