Sass has a few output styles. It sounds like you're looking for the "expanded" style.
nested
#main {
color: #fff;
background-color: #000; }
#main p {
width: 10em; }
expanded
#main {
color: #fff;
background-color: #000;
}
#main p {
width: 10em;
}
compact
#main { color: #fff; background-color: #000; }
#main p { width: 10em; }
compressed
#main{color:#fff;background-color:#000}#main p{width:10em}.huge{font-size:10em;font-weight:bold;text-decoration:underline}
I'm not familiar with the c9 editor but if there's a settings page (maybe try the cog icon in the bottom right of the editor), you may be able to toggle it there.