acel = Style[
  DisplayForm[
   RowBox[{SuperscriptBox["v", 2], "=",
     SubsuperscriptBox["v", "0", 2], "+ 2a [CapitalDelta]x",
     " [LongRightArrow] ",
     FrameBox[
      "a =" FractionBox[SubsuperscriptBox["- v", "0", 2],
        "2[CapitalDelta]x"], Background -> LightBlue]}]], 24, Black,
  Bold, FontFamily -> "Kalam"]

OpenerView[{"AAA", Style[acel, 30]}, Method -> "Active"]

OpenerView[{"AAA", acel}, Method -> "Active"]