WAB Dev Edition 2.7: How can I add a dropdown menu to header widget controller?

FrancescoTonini2

I am using WAB2.7 Dev Edition as a template, and am trying to add a dropdown menu item to the header widget controller element, where all the links are listed. For example (see image below), I would like users to click on the "sample data" link and have a list of N items in a drop-down menu fashion.

Sample Data

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Sample Data1  (link)

Sample Data2  (link)

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For CSS, I can probably re=use some of the jimu.css style (which one?) but for the functionality, I am looking inside the \themes\FoldableTheme\widgets\HeaderController\Widget.js file:

array.forEach(links, function(link) {