Followup for #4621, which unfortunately hadn't gotten enough enough browser testing besides Chrome/Firefox on OS X. I tested on Chrome, Firefox, Safari and IE11 in all modes down to IE7 on Windows and OS X.

• Hide the scrollbar on the TOC on all browsers. It was never the intention for it to be visible with the scroll indication in place. A wrapper element was necessary to achieve the desired effect.
• Fixed the scroll indication gradient on Safari, which was caused by the wrong from-color, which now matches the to-color.
• Fixed a issue in old IE where the TOC didn't render on the correct position through setting left: 0 and top: 0 on it.

cc: @nodejs/documentation