The main reason why I provided Horizontal Menu Layout, because not all End-Users are happy to use Vertical Menu Layout. Sometimes, some pages are good to be displayed with Horizontal Menu Layout.
You may simply switch from Vertical Menu Layout to Horizontal Menu Layout, by clicking on Theme Layout -> Horizontal. Yes, it's so simple and easy like that!
As you can see, when you are browsing the Web Application in Horizontal Menu Layout, then the Theme Selector contains the related settings to Horizontal Menu Layout. You can adjust the settings that suits your needs from that Theme Selector.
Another good news is, some of settings in Theme Selector that can be implemented for Vertical Menu Layout, will be used also for Horizontal Menu Layout. In other words, they will share the same settings between one to each other.
Please note, that in this demo site, when you are browsing via Desktop mode, then you will see submenu items under the Features menu item is too long. Therefore, some of submenu items cannot be seen properly due to the limited screen height. You should switch the Menu Layout from Horizontal to Vertical from Theme Layout -> Vertical for such case.
See? That's why Horizontal Menu Layout is not always good to be used in Dekstop mode. However, when you are browsing it via Phone mode, then this Horizontal Menu Layout is very good to display for such case above. ;-)