Popup Title Padding

https://github.com/Esri/dojo-theme-flat/blob/master/STYLUS/esri/dijit/css/Popup.styl#L80
https://github.com/Esri/dojo-theme-flat/blob/master/STYLUS/esri/dijit/css/Popup.styl#L418

In Popup.styl there's a `padding` rule for `.titlePane` that is set to `auto`, which isn't a valid value for `padding`. This rule is normally just ignored and doesn't seem to cause a problem, unless the stylesheets are run through a minifier like [cssmin](https://github.com/gruntjs/grunt-contrib-cssmin), in which case the `padding` rules are merged, i.e.:

```
padding: 6px;
padding-right: auto;
```

becomes:

```
padding: 6px auto 6px;
```

Is there a reason we're using `auto`? Should it be `inherit` or `initial` instead?