Operator issue

Hi - 

In _pure-drawer-global.scss I had to modify the following for it to compile

```css
.pure-toggle-label[data-toggle-label='right'] {
	right: 56 / 2 + px;
	left: auto;
}
```

to 


```css
.pure-toggle-label[data-toggle-label='right'] {
	right: (56 / 2) + px;
	left: auto;
}
```

--Matt