double arrows on the selection in the single product

Hi,

I've got a problem on the single product display, on the shop.
when you go for example on http://optique-export.fr/produit/gant-ga-4068/
when you need to select the size/color, on PC resolution, there is 2 arrows appears on the left, instead of one.
this is not the case on ipad resolutuion.
this sound not very serious.
could you please solve the bug?
please see the picture enclose
you still have your acess on my admin

thanks for your intervention
julie