How to make my webpage resiz-able?

Question

How to make my webpage which I have made resize-able so that when viewed in full or hal screen on computer or even when viewed on phone it just looks like it was zoomed or the webpage looks similiar?

For code please refer to my project Birthday Invitation webpage here on Sololearn.

Answer 1

Quantitanic

https://www.sololearn.com/post/455766/?ref=app

Answer 2

These threads will help you.

https://www.sololearn.com/Discuss/2108143/?ref=app

https://www.sololearn.com/Discuss/2162541/?ref=app