How do I get 3 buttons in header to stack vertically instead of side by side?

A couple of years ago, by searching the internet, I created 2 additional buttons to the header of this website by pasting code into Code Injection under Developer Tools<Settings and then adding the code below to CSS.  At the time, I couldn't believe it actually worked.  I'd now like the buttons to be stacked horizontally rather than side by side. When I change "horizontal" to "vertical"  in the CSS code nothing happens. Can anyone help with this? I didn't include the code I pasted into Code Injection because I didn't see anything in it in regard to orientation of the buttons.

/* begin add buttons to header */

  .header-actions-action.header-actions-action--cta {
  
    display: -webkit-box;
    display: -ms-flexbox;
    display: flex;
    
    -webkit-box-orient: horizontal;
    -webkit-box-direction: normal;
    -ms-flex-direction: row;
    flex-direction: row;
    
    grid-gap: 0.5em;
    gap: 0.5rem;
    
    }

/* end add buttons to header */

The website is www.shermanlibrary.org

Stacked like this?

Yes! Exactly!

That worked perfectly! Thank you Tuan!