How To Get Nested Nav Menu in line

I’m trying to get the navigation menu to have nested pages that drop down in a Straight Line as opposed to what appears to be the default nesting behavior of spreading them out laterally

here is a screen shot of the old non WP version of the site where the menu behavior is what I’d like to have:

https://www.dropbox.com/s/4ll7a4uatmvhycx/Nested%20Nav%20Menu.PNG?dl=0

and here is a screen shot of what the default WP 2017 theme does:

https://www.dropbox.com/s/txbrkuwbj8rspjo/Nested%20Nav%20WP%20twenty%20seventeen.png?dl=0

and here is a screen shot of the current wp dashboard

https://www.dropbox.com/s/lcc8m7rnp1p4evk/Nested%20Nav%20Menu%20%20Dashboard.PNG?dl=0

Is this a configuration thing that I missed or must I get a plugin to accomplish this?
thanks

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