There’s a bug on Google Chrome with the latest WordPress Dashboard. The bug has been submitted to WordPress’ bug tracker. However, the case is closed since the error occurs only in Chrome. Other browsers are rendering it just fine. There is a workaround by disabling “slimming paint” in Chrome.

Place this text in the URL of your Chrome browser:

chrome://flags/#disable-slimming-paint

Disable it.

The bug will remain until you restart Chrome.