I’m on my phone so this will be terse.
Mark the menu item as active if the menu item name equals current page title:
{{ $active = or $active (eq .Name $current.Title) }}
Mark the menu item as active if the current menu item name is Blog and the current page section is post:
{{ $active = or $active (and (eq .Name "Blog") (eq $current.Section "post")) }}
Mark the menu item as active if the current menu item name is Tags and the current page section is tags:
{{ $active = or $active (and (eq .Name "Tags") (eq $current.Section "tags")) }}
In the case of the Cupper theme, the menu item will be visually highlighted.