IE 8 and below don't understand `rgba` color values. I'll leave it up to you if you want to support IE 8. If you do, you just need to include a rule above the `rgba` rule with a standard hex color. So, you'd end up with:

```css
border-top: 1px solid #000;
border-top: 1px solid rgba(0, 0, 0, 0.5);