HELP! Collapsible Pages and Subpages

Hi there,

I was wondering if there was a theme or tutorial on how use css, xhtml, and php to get collapsible pages and subpages. Essentially, I am going to need something like this (https://www.sonoma.edu/it/) but only converted to wordpress.

As you can see, each active page has subpages like “IT HOME”

IT HOME
— Contact Us
— About IT
— Departments
— Policies
— Service Menu
— Training
Helpdesk
Computer Labs
Digital Media
etc……….

Notice how the other pages like “Helpdesk” also have subpages are not displayed? That’s because we are currently on the “IT Home” page and “Helpdesk” subpages don’t need to be displayed. It’s only when you click “Helpdesk” that you get to see all the subpages (https://www.sonoma.edu/it/helpdesk/)

In sum, I want active pages to show their sub pages, and inactive pages to hide their sub pages.

Once again, a theme or tutorial that shows exactly this would be a phenomenal help. Thanks in advance!