Fully Responsive Website Development using HTML/CSS and a bit of JS

It was a fun and quite easy challenge for me. However, there are some parts where I struggled a bit. I'm firstly looking for an overall and honest opinion from you and if you can suggest me something I could/should improve. I've had hard time trying to make those grid and background image assets responsive so If anyone has a good idea or solution, please share. I've tried to use width, height and position of images in percentage or vh/vw but it didn't turn out to work as I expected.