blog screen is cut off on the top side. when under 640px width.

Hi, I think I found a minor bug and report here.
In the blog menu of the sample site, the top side is cut out of the browser's view.
It's only shown when the width of screen is less than 640px.(usually mobile environment)
You can find the situation more clearly by clicking into a post with a featured photo.(maybe the 1st one in the sample site)

I really enjoy this beautiful theme and hope you can fix the display :)
Thank you for your effort.