"../" vs "/" for background image url? (would assume "../" is more proper, Rubymine doesn't understand though)

I'm unsure if I'm using bad syntax, or if Rubymine just shouldn't be complaining about this.  


For the code below, Rubymine lists two errors:
1) Can't resolve directory 'images;
2) Can't resolve file '25x25_group.png'

<div >  {code}  </div>

If I remove the two periods, Rubmyine is happy:
<div >  {code}  </div>

Either way works in a browser.  I would just assume that using "../" would be better syntact than just assuming the style will resolve the application root.  ?

Thanks!