 75,  15,
      50,  75,  15,
     -20,  45,  15,
      50,  45,  15,

    // middle rung
     -20,  15,  15,
      20,  15,  15,
     -20, -15,  15,
      20, -15,  15,

    // left column back
     -50,  75, -15,
     -20,  75, -15,
     -50, -75, -15,
     -20, -75, -15,

    // top rung back
     -20,  75, -15,
      50,  75, -15,
     -20,  45, -15,
      50,  45, -15,

    // middle rung back
     -20,  15, -15,
      20,  15, -15,
     -20, -15, -15,
      20, -15, -15,
  ];

  const indices = [
    