Image on GogelMap with Opacity 50%; I want GoogleMap on that image

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ASP.NET

CSS

I m having background img with opacity 50% on site.master which will be inherited to all forms.
In one of my form, i have added GoogleMap.

My Problem is:-

GoogleMap is below the img. Which make Google map as Transparent.

I want Google map on that img. Which CSS attribute will bring my solution

I have tried with

overflow:hidden;