[danieldon]

  Obsolete is a verb, but it is a poor choice. A better
  choice would be obsolesce, as in: "LESS.js will 
  obsolesce CSS"

"Obsolete" is the correct word because it's a transitive verb (eg, [subject] obsoletes [object]), while obsolesce is an intransitive verb (eg, [subject] obsolesces).

[GavinB]

I would have gone with "Less.js Will Render CSS Obsolete."