Some times using percentages for fluidity in layouts is tricky because you have to deal with containers and border-type things.
Look in to using viewport units and learn some thing about it on css-tricks and caniuse will show you how well it's supported.
Essentially you can say:
<div style="...
The way to change the cursor when it's over an NSButton:
First, you should subclass NSButton first, then add the code below:
@property (strong) NSCursor *cursor;
- (void)resetCursorRects {
if (self.cursor) {
[self addCursorRect:[self bounds] cursor: self.cursor];
} else {
...
