VTFlatAppearance.m

+ (void)customizeAppearance
{
    UIColor *lightColor = [UIColor lightGrayColor];
    UIColor *darkColor  = [UIColor darkGrayColor];

    // Navigation bar
    UIGraphicsBeginImageContext(CGSizeMake(1, 1));
    UIBezierPath *rectBezierPath = [UIBezierPath bezierPathWithRect:CGRectMake(0, 0, 1, 1)];
    [lightColor setFill];
    [rectBezierPath fill];
    [[UINavigationBar appearance] setBackgroundImage:UIGraphicsGetImageFromCurrentImageContext() forBarMetrics:UIBarMetricsDefault];
    UIGraphicsEndImageContext();
    [[UINavigationBar appearance] setTitleTextAttributes:@{
                               UITextAttributeTextColor : [UIColor whiteColor],
                         UITextAttributeTextShadowColor : [UIColor clearColor],
                                    UITextAttributeFont : [UIFont fontWithName:@"HelveticaNeue-Bold" size:20] }];
    
    // Bar button item
    CGFloat corner = 10;
    CGFloat cornerRadius = corner/2;
    UIGraphicsBeginImageContext(CGSizeMake(corner, corner));
    UIBezierPath *roundedBezierPath = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(0, 0, corner, corner) cornerRadius:cornerRadius];
    [darkColor setFill];
    [roundedBezierPath fill];
    [[UIBarButtonItem appearance] setBackgroundImage:[UIGraphicsGetImageFromCurrentImageContext() resizableImageWithCapInsets:UIEdgeInsetsMake(cornerRadius, cornerRadius, cornerRadius, cornerRadius)
                                                                                                                 resizingMode:UIImageResizingModeStretch]
                                            forState:UIControlStateNormal
                                          barMetrics:UIBarMetricsDefault];
    UIGraphicsEndImageContext();
    [[UIBarButtonItem appearance] setTitleTextAttributes:@{ UITextAttributeTextColor : [UIColor whiteColor], UITextAttributeTextShadowColor : [UIColor clearColor] }
                                                forState:UIControlStateNormal];
    [[UIBarButtonItem appearance] setTitleTextAttributes:@{ UITextAttributeTextColor : [UIColor grayColor] }
                                                forState:UIControlStateDisabled];
    [[UIBarButtonItem appearance] setTitleTextAttributes:@{ UITextAttributeTextColor : [UIColor whiteColor] }
                                                forState:UIControlStateHighlighted];
    
    // Back bar button item
    CGSize backButtonSize = CGSizeMake(20, 32);
    CGFloat headWidth = 12;
    UIGraphicsBeginImageContextWithOptions(backButtonSize, NO, [UIScreen mainScreen].scale);
    UIBezierPath *backButtonPath = [UIBezierPath bezierPath];
    [backButtonPath moveToPoint:CGPointMake(1, backButtonSize.height/2)];
    [backButtonPath addLineToPoint:CGPointMake(headWidth, 1)];
    [backButtonPath addArcWithCenter:CGPointMake(backButtonSize.width-1-cornerRadius, 1+cornerRadius) radius:cornerRadius startAngle:-M_PI_2 endAngle:0 clockwise:YES];
    [backButtonPath addArcWithCenter:CGPointMake(backButtonSize.width-1-cornerRadius, backButtonSize.height-2-cornerRadius) radius:cornerRadius startAngle:0 endAngle:M_PI_2 clockwise:YES];
    [backButtonPath addLineToPoint:CGPointMake(headWidth, backButtonSize.height-2)];
    [backButtonPath closePath];
    [darkColor setFill];
    [backButtonPath fill];
    [[UIBarButtonItem appearance] setBackButtonBackgroundImage:[UIGraphicsGetImageFromCurrentImageContext() stretchableImageWithLeftCapWidth:headWidth+1 topCapHeight:backButtonSize.height/2]
                                                      forState:UIControlStateNormal
                                                    barMetrics:UIBarMetricsDefault];
    UIGraphicsEndImageContext();
}