pure javascript, pure CSS.

Hey, great work on this one. On desktop layout, I think making each country card a bit smaller will be better because right now on my end, I only get 2 country card on a single row. I am using a 1366x768 monitor. The site is responsive though and the mobile state looks great.

Some other suggestions would be:

• Currently the theme toggle only works for mouse clicks because you aren't using any interactive elements on it. Remember when creating interactive component, interactive element should be used. On this one or in general when you are creating a theme toggle, you should use radio buttons that are inside a fieldset with a legend.Have a look at this simple snippet that I have implementing this one or you can see my solution on this same challenge. Let me know if you have any queries on this one.
• You don't need to use nav to wrapped the search and filter bar on the main tag. You should use form for the search bar since data is being manipulated on that one and to make the markup clear.
• Your input right now currently lacks associated label to it or an aria-label to which will define the purpose of the input element. Always include it so that user will know what they need to give on each input. Make sure that label is pointing to the id of the input as well.
• For the filter bar, again it is not accessible since you are not using interactive elements. For this one, you can use a select tag, though it can't be styled I think? But it will be better than the current implemented one. Another approach would be to use a role="listbox" on this one. You can see that implementation on my solution as well.
• Also, your filter dropdown is not being hidden properly. Right now, it is only hidden visually by using transform but it is still being picked up by assistive tech. Add an extra visibility: hidden on the hidden state and use visibility: visible when the dropdown is being shown.
• For each card, the :hover state for me is too much. It scales the element too big, a subtle one would be much better than overdoing it.
• Since you are making the country card a link, use a tag for this one and not just div. Remember, when a component navigates a user on another page, a tag should be used. For this one, you should only use the a tag to wrap the img and make sure that the a tag is not containing the full country card because that will be an invalid markup. Another approach would be to use like a ::after of the a tag to occupy full height and width of the country card so that it will be clickable.
• For those 3 information about the country, as you can see they are "list" of information so it would be nice to use ul on those one.

VISITING A COUNTRY(on your app):

• The go back should be also a link and not a button since it directs a user in a another page. button are for control and a tag are for links.
• Also, I instantly get a mobile state view for the page, your breakpoint on that one is too big I think, toning it down would be really nice.
• Your country image is missing the alt attribute. When using img tag, do not forget to add the alt attribute, whether the value is empty or not. Because by not including it, screen-reader will instead read the source path of the image which you don't want. So always include it.
• You can use h1 for the country name on this one since it is all about the specific country when visiting one so it makes sense to use h1.
• Again, those 8 items are "list" of information about the country so using ul would be nice.
• When wrapping up a text-content, make sure that it is inside a meaningful element like p tag or heading tag and not using like div, span to wrap the text.
• For the name border countries you can use a heading tag on that since it gives information about what the section will contain.
• Those border-countries as well should be using a tag since they are links to view a another country. There are lots of usage of not accessible elements on this one which are treated as interactive.

But still, great job again on this one.