fix code block on mobile

Hey, I like how the `.highlight` code block looks like. It's like a silk gift wrap.

But there's too much padding on the left, when nested in a list or on a small screen. 

And the `<ul>` tag on chrome has `-webkit-padding-start` set to `40px`. The reset is added.

I updated the style.scss a little bit.

I've tested it on different screen size. It would affect the layout on bigger screens.

Thanks.

### Before.

![2014-01-28-230741_320x516_scrot](https://f.cloud.github.com/assets/469551/2026713/a17bcb72-889b-11e3-81d6-b5702c0b516b.png)


### After.

![2014-01-28-230736_320x516_scrot](https://f.cloud.github.com/assets/469551/2026733/264b95c6-889c-11e3-95a4-1daae4b5fd88.png)