I know the close button closes the lesson, yet every time I go to sentence view, I click that close button to get back to reader view. Suggestion: I treat "Sentence view" as a modal. Maybe it a modal, with an X (top right) to close i. This is how I treat it regardless of the fact that I know it's not a modal, so IMO this would be the intuitive choice. The "X" in the lesson makes me think I'm in a "temporary place". Firstly, I'm not sure it's even necessary, as I can just click "Lessons" to return home. Secondly, a "Home" icon would be more intuitive, or the word "Home" with a "<--" arrow, as a Lesson is not really a temporary place, so every time I click the X I'm confused when I end up back on the homepage. I do this pretty much every day. This is on web, as the mobile app _does_ treat sentence view as a modal