Hello Iryna,
Just checked your work, it looks kind of cool. I like the colour scheme, good theming.
It has some small issues you may fix.
Age input comes without label tag, please fix.
Same two radio buttons come without label, the first radio has one wrong label associated, please fix.
You may not place a non label content inside label tag, check line 72 as following
<label for="interest">Your interests:</label >
No need to host this text with a label since it’s not a label.
Page layout is broken for mobile device, check:
This is becasue you set
min-width: 320px; for your body tag, please remove it.
For mobile I think the padding/margin for the form is a little too much. Give it less padding/margin to utilize more space for page content.
The combobox, I suggest you add one disable/hidden as default element.
Adding some more space between checkbox buttons in mobile view could be great.
I think the border you gave to the checkbox buttons is out of page design.
I also suggest make the submit button more sharp. Give it a sharp background colour(like background colour of the page), and maybe bold text.
I think if you place radio buttons vertically(each in line) rather horizontally(next to each other) could be better.
Also giving some padding for text field, textarea and combobox would be great.
I also see you set the global font-size as 20px, please don’t. Don’t use px for font-size.
It’s better using absolute/absolute-relative unit like em/px for border-radius. When you set border-radius:5%, it takes 5% of width for top radius, and 5% for height radius, so it looks broken(weird) when screen is wide or tall. what about border-radius:1em?
You may have a quick read on this survey form challenge walkthrough article for more tips and better explanation of things I mentioned.
Overall good work, like the design.
keep going on great work, happy coding.