Adding downloadable buttons with URL after adding HTML code

Hi there, 

I was wondering if anyone could help. I am trying to add html elements of code in my blog post to lock a file using this instructions.

Now within that I want to add a button on the HTML code or a coloured box that's noticeable that reads as 'Download Now' with a link to a URL for people to click on.

How do I do that?

@tuanphan do you have any solution for this?