Red, boxed markup

\version "2.13.2"

\new Staff {
   \set Score.proportionalNotationDuration = #(ly:make-moment 1 16)
   c'4
   \override TextScript #'staff-padding = #4
   \override TextScript #'self-alignment-X = #left
   c'4 ^ \markup \with-color #red \override #'(box-padding . 1.0)
      \box \hcenter-in #3 \line { 2 / 3 }
   c'4
   c'4
   \bar "||"
}