Coming soon page mobile first using html css js

Should i even be trying to make these challenges responsive or just work hardcoded on 375 and 1440 sizes? I don't like the fact that i add all-around padding to make it look good on desktop but then it's impossible to make it responsive on smaller sizes unless im just really bad at css and close-minded. I also feel like i have some problems with flexbox and it was hard for me to make the image and the left panel hit their desired sizes. Looking for every bit of advice so i can improve and continue my journey with frontend, thanks in advance!