Farther than level 20?

I have seen some recent pictures where the person is level 20 but has more green filled in on the bar on the top left. What is with that? Can you level farther than 20?

Sort of. Even after you reach level 20, you can continue to fill your green bar with experience. Each time you fill it completely, you earn another skill point, and it goes back to zero. Skill points can be used to buy more skills. Since you can only ever use eight skills at a time, this additional "leveling" doesn't make you any more powerful, but it does make your more versatile. This allows for continued character advancement without making them more powerful, preserving the game balance and the ability for newer players to compete.