Scala version conflict

I have following build.sbt file

name := "Server"

version := "1.0"

scalaVersion := "2.11.8"

libraryDependencies += "io.reactivex" %% "rxscala" % "0.26.1" withSources()

libraryDependencies += "org.scalafx" %% "scalafx" % "8.0.60-R9" withSources()



fork := true

javaOptions += "-Xmx2G"

Everything is fetched correctly. But when I try use scala fx in IDE. Ide can not use it. For example import rx.lang.scala.Observer is incorrect.