How to build second level of DEDUCE navigation bar

I’m using R Shiny to build a website that helps designing clinical trials. I would like to create a second level of navigation to the page by using the navbarMenu() function, but only one line of the second level is able to be seen, limited to the space of navigation bar. Figure 1 is what I expect of second level of navigation. Figure 2 is the current navigation bar by using the function. I’ll have to scroll down to see the whole dropdown list. Do you have any ideas how I could get all rows of this dropdown list to appear, and overlap the photo?

Here is the website for you to review the problem. Once you click “CONDUCT YOUR TRIAL_test” button, you have to scroll down to see the whole dropdown list. (https://nanchen.shinyapps.io/DEDUCE/)

Here is the code I used to create a second level of navigation to the page.

Ui <- page_navbar(

navbarMenu("CONDUCT YOUR TRIAL_test",
tabPanel("Manually enter patient data"),
tabPanel("Upload CSV file"))
)

Figure 1. Target second level of navigation

Figure 2. Current second level of navigation