You can look on the web for ready made css layouts ( templates are probably not what you want ) that are mobile friendly; most new ones are these days.
You can setup one you like with an online designer like: https://www.thesitewizard.com/wizards/layout.shtml
I initially learnt html with a Dummies book and like you checked how things worked on other peoples sites.
For server based websites I personally prefer using my own as I can do what I want with it and it is not restricted by what for instance Blynk have installed.
I currently have a website where I can upload environmental data and it is saved to a database and displayed in different ways: http://rubblewebs.co.uk/IOT/
I have a rout tracker page where my data is overlaid on a Google map: https://rubblewebs.co.uk/IOT/manchester.html
I also have a webpage where the current outside temperature is saved and my "clock" downloads it every 15 min and another with a binary file that another devices I have checks every night to see if there is new firmware to download.
Good luck with your projects and there are web design forums around that can help you. I use https://www.sitepoint.com/community/
I am not great with JavaScript but will have a look over your html later.