Set overlay when dropdown appears on screen

I have a drop down button and when user clicks on it dropdown appears which is a tableview that is hidden.

- (IBAction)showDropDown:(id)sender {
    self.tableView.hidden = NO;
}

Now i want to set entire screen overlay to 66% just like a blurry screen only excluding button and tableView. They must be visible clearly. And when user made as selection...

-(void)tableView:(UITableView *)tableView didDeselectRowAtIndexPath:(NSIndexPath *)indexPath{
    self.tableView.hidden = YES;
}

And everything will be same again.