Каковы секреты CSS для гибкой / плавной HTML-формы?

var cars = [
  {
    "makes"  : "Honda",
    "models"  : ['Accord','CRV','Pilot']
  }, 
  {
    "makes"   :"Toyota",
    "models"  : ['Prius','Camry','Corolla']
  }
];

$(function() {
  vehicles = [] ;
  for(var i = 0; i < cars.length; i++) {
    vehicles[cars[i].makes] = cars[i].models ;
  }
  var options = '';
  for (var i = 0; i < cars.length; i++) {
    options += '<option value = "' + cars[i].makes + '">' + cars[i].makes + '</option>';
  }
  $("#make").html(options);   // populate select box with array

  $("#make").bind("click", function() {
    $("#model").children().remove() ;   // clear select box
    var options = '';
    for (var i = 0; i < vehicles[this.value].length; i++) {
      options += '<option value = "' + vehicles[this.value][i] + '">' +
        vehicles[this.value][i] +
        '</option>';
    }
    $("#model").html(options);   // populate select box with array
    $("#models").addClass("show");
  });     // bind end
});

.hide {
  display: none;
}
.show {
  display: inline;
}
fieldset {
  border: #206ba4 1px solid;
}
fieldset legend {
  margin-top: -.4em;
  font-size: 20px;
  font-weight: bold;
  color: #206ba4;
}
fieldset fieldset {
  position: relative;
  margin-top: 25px;
  padding-top: .75em;
  background-color: #ebf4fa;
}
body {
  margin: 0;
  padding: 0;
  font-family: Verdana;
  font-size: 12px;
  text-align: center;
}
#wrapper {
  margin: 40px auto 0;
}
#myFieldset {
  width: 213px;
}
#area {
  margin: 20px;
}
#area select {
  width: 75px;
  float: left;
}
#area label {
  display: block;
  font-size: 1.1em;
  font-weight: bold;
  color: #000;
}
#area #selection {
  display: block;
}
#makes {
  margin: 5px;
}
#models {
  margin: 5px;
}

<script src = "https://ajax.googleapis.com/ajax/libs/jquery/1.8.0/jquery.min.js"></script>

<div id = "wrapper">
  <fieldset id = "myFieldset">
    <legend>Cars</legend>
    <fieldset id = "area">
      <label>Select Make:</label>
      <div id = "selection">
        <div id = "makes">
          <select id = "make"size = "2"></select>
        </div>
        <div class = "hide" id = "models">
          <select id = "model" size = "3"></select>
        </div>
      </div>
    </fieldset>
  </fieldset>
</div>