Theme Horse

hi
for this you need code customization. I think adding css doesn’t work. you need to customize the code inside library->structure->header-extension.php under this function attitude_home_slogan() function
you need to add target= _blank inside tag.
we recommend not to change the code because while updating to our new version all your customization code will be lost. So better create a child theme and unhook the function first and then you may change the code.
thank you