macosx: Declare standard size of small side of scrollbar in VLCLibraryUIUnits

Signed-off-by: Claudio Cambra <developer@claudiocambra.com>

modules/gui/macosx/library/VLCLibraryUIUnits.h

@@ -30,6 +30,8 @@ NS_ASSUME_NONNULL_BEGIN
 + (CGFloat)standardSpacing;
 + (CGFloat)smallSpacing;
 
++ (CGFloat)scrollBarSmallSideSize;
+
 @end
 
 NS_ASSUME_NONNULL_END

modules/gui/macosx/library/VLCLibraryUIUnits.m

@@ -39,4 +39,9 @@
     return 5;
 }
 
++ (CGFloat)scrollBarSmallSideSize
+{
+    return 16;
+}
+
 @end

modules/gui/macosx/library/VLCLibraryWindow.m

@@ -285,11 +285,14 @@ static void addShadow(NSImageView *__unsafe_unretained imageView)
     [self setViewForSelectedSegment];
     [self repeatStateUpdated:nil];
     [self shuffleStateUpdated:nil];
-    
-    const CGFloat scrollViewTopInset = 16.;
+
+    // We want all the insets to look even, and since the scrollbar is transparent,
+    // we have to compensate for this on the sides where there isn't a scrollbar to
+    // match up the perceived whitespace on all sides
+    const CGFloat scrollViewTopInset = [VLCLibraryUIUnits scrollBarSmallSideSize];
     const CGFloat scrollViewRightInset = 0.;
-    const CGFloat scrollViewBottomInset = 16.;
-    const CGFloat scrollViewLeftInset = 16.;
+    const CGFloat scrollViewBottomInset = [VLCLibraryUIUnits scrollBarSmallSideSize];
+    const CGFloat scrollViewLeftInset = [VLCLibraryUIUnits scrollBarSmallSideSize];
 
     // Need to account for the audio collection switcher at the top
     const CGFloat audioScrollViewTopInset = scrollViewTopInset + _optionBarView.frame.size.height;