If it’s only CSS tweaks you need (and no other theme-file edits), you don’t need a child theme. ?? You can use a custom CSS plugin instead, like the Custom CSS module in Jetpack, or a standalone plugin as sacredpath linked above.
I strongly recommend moving your CSS tweaks out so you’ll be able to update the theme going forward. There are often important issues, including security holes, fixed in new versions of a theme. Version 1.4.1 fixes one such security problem. Until you’re able to move your CSS tweaks into a custom CSS plugin, you should remove this file from your server as soon as possible:
ryu/genericons/example.html
I know it may take some time to move the changes out into a custom CSS plugin, but think of it this way: it’ll surely take less time than cleaning up a hacked site. ??
Good luck!