Skip link > Remove tabindex

What does this MR do?

Removes tabindex="1" from the navigation skip link.

• Since it’s the first focusable item in the DOM it doesn’t need tabindex.
• The use of a positive tabindex isn’t recommended and can negatively impact focus management (Read).

Before	After
<a class="sr-only gl-accessibility" href="#content-body" tabindex="1">Skip to content</a>	<a class="sr-only gl-accessibility" href="#content-body">Skip to content</a>

Screenshots

No visible change.

Does this MR meet the acceptance criteria?

Conformity

• Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

N/A

Security

N/A

Related to #323483 (closed)