There are many great demonstrations of codes at Codepen website, but I have decided to pick only those with pure CSS3. Here 10 great CSS3 demos at codepen for everyone to see.
CSS Fractal pattern
Kenny Lindahl utilizes the potential of CSS3 to create this great looking animated flower like pattern.
CSS3 Logo Android
CSS3 Cat Smiling
A cute cat smiling and blinking his eyes purely creaded with CSS3 by Nicolas Slatiner
CSS3 Black Navigation Menu
Black Navigation Menu created by Sara Soueidan, only using CSS3.
Earth and Moon
Created by mutukrish, this is another great example of CSS3. Earth and Moon and space was created entirely with CSS3.
Social Switch Book
Social switch book is another great CSS example with flip animates on hover.
Parallax backgrounds with Cat Walk Cycle
Created by Rachel Nabors, experiment uses multiple background and cat walk cycle with pure CSS3 animation, creating a multi-depth parallax effect.
Rotating Chromo Icon
Nice CSS Chromo Icon that shrinks and rotates.
Mona Lisa with pure CSS
This epic portrait of Mona Lisa is not a picture file, it was created purely with CSS by Jay Salvat. It shows the capability of CSS3.
Old Woman Face, Pure CSS
Pushing the limits of CSS3, Brian Gonzalez converted this Old woman’s face in pure CSS with help of ruby code.