featured column font size

This media query is missing a closing bracket }:
https://www.screencast.com/t/Xf0dIUsJ

And this CSS selector is still missing an opening bracket as mentioned above:
https://www.screencast.com/t/dRaXjlJtZm

I have pasted David's code as Leo also suggest but it is NOT working for mobile font, the desktop version is good.

As Leo suggest this

This media query is missing a closing bracket }

I applied this and it works for mobile but it breaks the desktop font (means h2 font-size gets smaller like grid posts) and when I remove closing bracket, h2 font size works in desktop version but it breaks for mobile.

I took another quick look and you still have a whole bunch of syntax errors.

For example, all of the lines below are missing ;:
https://www.screencast.com/t/AATykSA1vK

There are several other mistakes as well.

You will need to spend some time going through your own CSS to make sure they are absolutely no syntax errors - this is not something we can help within this support forum as we are not a CSS helpline.

This service should also help to catch mistakes as well:
https://jigsaw.w3.org/css-validator/#validate_by_input