gistfile1.m

// ViewController.m

// Use at top
#import <QuartzCore/QuartzCore.h>

//...

// Add below the @implementation
- (void)loadView {
    [super loadView]; // important to have this call, otherwise things might not load
    NSLog(@"load view");
    
    self.starButton.layer.cornerRadius = 20; // this value vary as per your desire
    self.starButton.clipsToBounds = YES;
}