Just help with this website I am creating, please?

It is roughly halfway done. This is my codepen link - https://codepen.io/Rosstopherrr/full/eYNYVPG

I don’t know how you all start first when creating a website, but what I have learnt by watching tutorials is when coding with a live server on the browser is a small screen because obviously the visual studio is taken most of your window space and the browser on the right will be small screen size like a mobile device size.

Anyway, I just want you all to see what I am doing is right? Because when I inspect the page it is annoying wrong…

laptop view - this is the way I like it and want it to be like

the small mobile view is all wrong

I have taken screenshots because codepen is not showing the right polygon shapes for my images? And as you can see on the second screenshot, the polygon shape has now turned into a much smaller shape like almost a triangle shape!

What is the best solution for this? Have I complicate myself on this??