Buttons missing on exercises

Hi  

I'm having a problem with the matching section of the excercises on elementary - the matching buttons are not loading up.  

However, the buttons are present in the matching section.  

This holds tru for me on both Chrome and Firefox.

Is this a general issue on the site at present?

As an example, see below

• 电子邮件
  
• 坏了
  
• 发件箱
  
• 最好
  
• 跟