Could you share screenshot of this? It’s quite possible that you clicked the collapse sidebar button available, which you’ll have to click again to show the sidebar.
I just opened the URL and didn’t even make a single click on the webpage. I didn’t use Chrome because I use Safari to sync my bookmarks between my computer and my phone. I also don’t want to install an additional app.
Looks like responsive design. It will hide the navigation bar whenever it thinks your browser width is too small. When that happens, try the “hamburguer menu” on the top left.