There's nothing wrong in the code you posted, as far as I can tell - it passed for me :)
I did notice that forgetting to close the CSS rule above it will result in the error you're getting. Do you think that might be the problem?
If that doesn't fix, or isn't, your issue please post and format all of your HTML and CSS code so we can help you :)
You can format code by selecting it all while in the post editor, and pressing
Ctrl/Cmd + K, or by adding a new line and three backticks (
`) before and after your code, like this:
<code> will show up properly here