You’re also missing the opening quote:
@import url("../patchwork/style.css");
Ensure you’re following the directions here to the letter.
Sunny.css won’t be automatically replaced with your child theme’s sunny.css–only core WordPress theme files (index.php, header.php, footer.php, etc.) do this.
If you want to overwrite sunny.css in your child theme, you need to create both the CSS file and a functions.php file to enqueue the stylesheet. You can see an example of how stylesheets are enqueued by looking at the parent theme’s functions.php. This thread has some useful information from a user who’s done this with a different theme.
That said, depending on what you’re trying to do, it might be easier to add any CSS rules to your child theme’s style.css. Sometimes you can use the !important declaration to your rules to force them to override the other stylesheet, although this isn’t a best practice.