My apologies, I didn't see your message on time. I used the default Chrome browser on my OnePlus One running CyanogenOS 13 (Android 6.0). I should have posted this in my first comment itself.
Interestingly, I did not see any horizontal scrolling when I tried in Chrome browser (Mac OSX 10.11.4) in regular user mode. But on toggling device mode (in dev tools), and selecting one of the mobiles - Galaxy S5 or Nexus 6P, the horizontal scrolling started to appear, and it is a lot worse than on my actual android phone.
I haven't yet been able to identify the element that overflows, but the <html> and <body> seems to take default 100% width and are expected to be contained within the browser frame. There is some other rogue element, somewhere nested inside, which is causing this unwanted horizontal scrolling.
Interestingly, I did not see any horizontal scrolling when I tried in Chrome browser (Mac OSX 10.11.4) in regular user mode. But on toggling device mode (in dev tools), and selecting one of the mobiles - Galaxy S5 or Nexus 6P, the horizontal scrolling started to appear, and it is a lot worse than on my actual android phone.
I haven't yet been able to identify the element that overflows, but the <html> and <body> seems to take default 100% width and are expected to be contained within the browser frame. There is some other rogue element, somewhere nested inside, which is causing this unwanted horizontal scrolling.