Yellowstone is a nice GTK 3.x theme which looks like Mac OS X 10.10 Yosemite. Yellowstone theme will make your Elementary OS Luna looks like Mac OS X. We can add some other items such as Super Wingpanel and use the light panel plank theme. Here are some screenshots of my Elementary OS Luna with yellowstone theme installed.
If you like the above style, you can change your own Elementary OS Luna into Yosemite looks by installing Yellowstone GTK 3.x theme.
A. Download Yellowstone theme
Click here to download Yellowstone GTK theme. Next extract the .zip file you just downloaded. You will find there are several folders. Simply move or copy the folder yellowstone to /usr/share/themes. You can use the following command to move the folder.
sudo mv yellowstone /usr/share/themes
Now you can change the Elementary OS Luna theme using Elementary Tweaks. Don’t know how to install Elementary Tweaks? Read it here.
Ok we are done setting up the GTK theme. But we still need more tweaking to get the above result.
B. Install Ieos7 Icon theme
Ieos7 icon theme is a very nice icon theme for Elementary OS Luna. You can read how to install it on Elementary OS Luna from here. You can use Elementary Tweaks to set the icon theme.
C. Install LightPanel theme for Plank
Use this command to install Lightpanel theme for Plank:
sudo apt-get install plank-theme-pantheon elementary-plank-extra elementary-plank-themes
Now open Elementary Tweaks again and click Plank. Select LightPanel from the Theme list.