Header navigation border design

[jhancock532]

Makes minor adjustments to the header navigation design.

• Add missing colour variable for light mode hover state
• Add missing cursor pointer for switch toggle
• Swap from left border to pseudoelement for better border radius effect

See screenshots

Light mode

Dark mode

[chris-lawton]

Thanks @jhancock532 - this looks good!

One thing I did spot when testing in Forced Colors mode is that we've lost the underline on the top level menu links + the links that appear in the drop downs.

For the primary nav menu items we have the mixin here https://github.com/torchbox/torchbox.com/blob/migration-2026/tbx/static_src/sass/components/navigation/_primary-nav-desktop.scss#L63 but I think text-decoration: none has been added here https://github.com/torchbox/torchbox.com/blob/migration-2026/tbx/static_src/sass/components/navigation/_primary-nav-desktop.scss#L75 which is causing the mixin not to work.

For the items in the dropdowns it looks like we just need to include the mixin for the following classes: primary-nav-dropdown__row-link, primary-nav-dropdown__card-link

If you haven't got time then I can pick this up!