I think the era of multi-level menus is now very much over. This is due to the large number of people that now browse the internet on mobile devices. In many respects, this is a good thing as it forces us to be a little more creative in how we get site visitors from one place to where they want to be without tying up too much screen real-estate at the top of the screen.
Sadly, in Sparkle we don’t yet have a toggle visibility option which could bring a sub menu into view in the form of a page-width box containing text or button links. Neither do we have a modal option that could display button or text links in a pop-up modal. So, the best option would be to forgo the drop-down menus altogether and use an interim page instead for the main link. The interim page can then contain a series of button links to the sub pages. This would clearly be a better option for those with touch screen devices as the links could be a set of buttons that are more easily targeted with stubby fingers. It adds an extra page to your site for each multi-level menu, but it should be a whole lot easier for your site visitors to get around. The interim page would also allow for site expansion later if you wanted to add further links. This is how the interim page could look.
Or Maybe circular buttons would be better:
If you did go this route, I would also recommend adding a previous and next button at the bottom of each article page so visitors could step through the articles in date order without having to go back to the interim selection page. It would look something like this: