fixing border in NavSecondary

[stephiescastle]

Checklist

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Description

Fixes a v3 regression on NavSecondary borders . When scrolling down, secondary navigation should have a bottom border.

Instructions to test

• easiest to test with content on development

Tested in the following environments/browsers:

Operating System

• macOS
• iOS
• iPadOS
• Windows

Browser

• Chrome
• Firefox ESR
• Firefox
• Safari
• Edge