Icon for additionalSignupField for Lock

I’m trying to add custom sign up fields as a part of universal login. I found the parameter to add for these fields which is easy/great. However I’m having a hard time trying to understand where I’m supposed to source the icons from that fit with the Auth0 existing icons. This is what I have added to my universal login:

      additionalSignUpFields: [{
      	"name": "mobile",
        "placeholder": "your phone number (eg. +61412345678)",
        "icon": "https://raw.githubusercontent.com/feathericons/feather/master/icons/smartphone.svg"

And this is the result:


I guess the mismatch of the colour can’t be helped, but its positioning is also off. Auth0 offers this icon field but no guidance around how to actually use it properly. I’ve tried other icons but it just gets worse (icon isnt constrained to the grey box).