overwrite design of select menu in ios web browsers

I am web designer. I recently design a select menu for my one of client. select menu have 4 different countries with flags. i use [Custom Select box][1] for display the flag. but when i open my site in Apple iphone then select menu goes to his default design. So any one can me explain or give me the solution for the below issue. Please check below screen shots

when someone open it in iphone then view will be shown in image [![iphone view before select][3]][3]

after selection flag image will be disappear