WordPress fix Higghllight top level button when subpages are selected

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Higghllight top level button when subpages are selected, by robmcp

Any suggestions on this

Info Page (top level menu page)
Option 1 sub page
Option 2 sub page
Option 3 sub page

If I select Info Page in the menu, I can highlight/make active the button green red, whatever.

If I select subpages Options 1,2, or 3 which are NOT displayed in the menu ( Too many) then Info Page button (obvs) stops being highlighted Green or whatever colour.

Is there a way I can easily KEEP Info Page button Highlighted (active) regardless of which sub item I click on, unless I select another unrelated page.
Thanks in advance. McP

Higghllight top level button when subpages are selected