Up until Ubuntu went public with Unity, out-of-the-box Linux has always been rather ugly compared to both Windows and Mac. (And depending on who you ask, Ubuntu's Unity was even a step in the wrong direction!)
If you recently switched from Mac to Linux, or if you're just a regular Linux user who happens to like the aesthetics of Mac, the good news is that you can do something about it -- by using the Gela Theme.
The Gela Theme is one artist's response to the plethora of dark themes available to the Gnome desktop environment. This artist fought back with a bright-colored theme built on the fundamentals of clean lines and minimalist design.
The result is a Gnome theme that looks and feels like Mac on Linux. It's not an exact replica, but it's close enough that it evokes the right emotions.
An alternative to the Gela Theme would be to switch distros to Elementary OS Freya, which has a unique desktop environment that feels incredibly close to Mac without needing any tinkering on your part. But if we're being honest, we still prefer the Gnome-based desktop environment MATE.