HTML : How to add scroll bar to webpage?

HTML : How to add scroll bar to webpage?
To Access My Live Chat Page,
On Google, Search for "hows tech developer connect"

I promised to reveal a secret feature to you, and now it's time to share it.
This is a YouTube's feature which works on Desktop.
First, Make sure this video is playing.
Then, type the letters 'awesome' on the keyboard.
It will change your youtube progress bar into a flashing rainbow.

Allow me to introduce myself briefly,
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I help you answer your questions.
HTML : How to add scroll bar to webpage?
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: add scroll How webpage? HTML to to bar