Hey, Mengho! Hearthstone on MacOS has a minimum requirement of Sierra 10.12. Yosemite (10.10) and El Captain (10.11) are no longer supported to run Hearthstone.
We’ve seen issues with the graphics on systems that are below the system requirements on this thread.
If the system is within minimum requirements for Sierra, the graphics/card not showing properly should be fixed after upgrading to Sierra.