Write custom CSS via theme settings without re-write previous value [solved]

I try to creating an advanced theme settings for my theme but stuck on this problems (all done except this one), I write a value in my custom CSS but it rewrite the previous value every time I save the configurations. Let say I want the user can creating unlimited button style for every menu IDs, so I provide two field; first is text field for the menu IDs, and the second text field is for url from the image.

So user only adding the menus IDs and the images url then put the menu block to specific region, and they have new button style!

How can I do this? and can I do this via theme settings? If I can creating new CSS via theme settings without re-write previous value than it would be very flexible.

Update: issues solved.

Thanks,
Dan