Ah yes, the Outsiders!
The main theme of The Outsiders is social and class conflict. This theme is shown between the two gangs, the Socs and the Greasers. Some of the differences shown are values, socioeconomic status, wealth, and etc. But how do these differences play into the theme of social and class conflict? Well, the Socs are the wealthy portion of the people in the 1960s, and the Greasers are the poor/and or underprivileged portion of the people in the 1960s. Both of these groups don't necessarily get along too well. The main reason for this is their stance in the population.
Hope this helps!