Interesting, you remind me of another Ian.
All browsers (Chrome, Safari, Firefox, etc.,) have responsive simulation tools (within their Dev Tools) for perceived viewing of sites on different devices, aspect ratios, custom settings etc. You can also script the browser window itself to resize to specific dimensions. If you’re not able to do that most browsers also have extensions developed by others available.
I’ll let you Google those things since you will no doubt deem things unhelpful as you have already done for each response which is an interesting approach to seeking help from others.
By the way how is your Lock Orientation coming was all that also not helpful?