If I apply the following rule to an input element with id `#one` then the placeholder color will change, 

```
#one::-webkit-input-placeholder {
  color: red;
}

```

But if I use comma separater to combine placeholder rules of different browsers then the color doesn't apply, e.g. 

```
#two::-webkit-input-placeholder,
#two::-moz-placeholder{
  color: red;
}

```

Working example:

```css
#one::-webkit-input-placeholder {
  color: red;
}

#two::-webkit-input-placeholder,
#two::-moz-placeholder{
  color: red;
}
```

```html
<input id="one" type="text" placeholder="one">
<input id="two" type="text" placeholder="two">
```

Why does the `#two` placeholder not change its color to red?