phpdroid/pages/calculator.php

<div class="container">
  <fieldset id="container">
    <form name="calculator">
      
      <input id="display" type="text" name="display" readonly>
      
      <input class="button digits" type="button" value="7" onclick="calculator.display.value += '7'">
      <input class="button digits" type="button" value="8" onclick="calculator.display.value += '8'">
      <input class="button digits" type="button" value="9" onclick="calculator.display.value += '9'">
      <input class="button mathButtons" type="button" value="+" onclick="calculator.display.value += ' + '">
      <br>
      <input class="button digits" type="button" value="4" onclick="calculator.display.value += '4'">
      <input class="button digits" type="button" value="5" onclick="calculator.display.value += '5'">
      <input class="button digits" type="button" value="6" onclick="calculator.display.value += '6'">
      <input class="button mathButtons" type="button" value="-" onclick="calculator.display.value += ' - '">
      <br>
      <input class="button digits" type="button" value="1" onclick="calculator.display.value += '1'">
      <input class="button digits" type="button" value="2" onclick="calculator.display.value += '2'">
      <input class="button digits" type="button" value="3" onclick="calculator.display.value += '3'">
      <input class="button mathButtons" type="button" value="x" onclick="calculator.display.value += ' * '">
      <br>
      <input id="clearButton" class="button" type="button" value="C" onclick="calculator.display.value = ''">
      <input class="button digits" type="button" value="0" onclick="calculator.display.value += '0'">
      <input class="button mathButtons" type="button" value="=" onclick="calculator.display.value = eval(calculator.display.value)">
      <input class="button mathButtons" type="button" value="/" onclick="calculator.display.value += ' / '">
    </form>
  </fieldset>
</div>
<script>
var parent = window.parent;
console.log("Calculator parent is "+parent+", and they are happy!");
function message(text){
  if(text.includes("event:back")){
    parent.postMessage("open:pages/home.php", "*");
  } else if (text.includes("event:menu")){
    console.log("menu clicked (but it don't have any event in calculator)");
  }
}
window.addEventListener("message", receiveMessage, false);
var reference;
var data;
function receiveMessage(event)
{
  
  
  reference = event.reference;
  data = event.data;
  message(data);
}
</script>
<style>
body {
  background: url(http://www.inkspilldesign.com/demo/wood-tile-background.jpg);
  background-color: #424242;
  font-family: Tahoma;
  max-width: 100%;
  max-height: 100%;
  width: 100%;
  height: 100%;
}

.container {
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  width: 100vw;
}

#container {
  width: 200px;
  padding: 8px 8px 20px 8px;
  margin: 20px auto;
  background-color: #ABABAB;
  border-radius: 4px;
  border-top: 2px solid #FFF;
  border-right: 2px solid #FFF;
  border-bottom: 2px solid #C1C1C1;
  border-left: 2px solid #C1C1C1;
  box-shadow: -3px 3px 7px rgba(0, 0, 0, .6), inset -100px 0px 100px rgba(255, 255, 255, .5);
}

#display {
  display: block;
  margin: 15px auto;
  height: 42px;
  width: 174px;
  padding: 0 10px;
  border-radius: 4px;
  border-top: 2px solid #C1C1C1;
  border-right: 2px solid #C1C1C1;
  border-bottom: 2px solid #FFF;
  border-left: 2px solid #FFF;
  background-color: #FFF;
  box-shadow: inset 0px 0px 10px #030303, inset 0px -20px 1px rgba(150, 150, 150, .2);
  font-size: 28px;
  color: #666;
  text-align: right;
  font-weight: 400;
}

.button {
  display: inline-block;
  margin: 2px;
  width: 42px;
  height: 42px;
  font-size: 16px;
  font-weight: bold;
  border-radius: 4px;
}

.mathButtons {
  margin: 2px 2px 6px 2px;
  color: #FFF;
  text-shadow: -1px -1px 0px #44006F;
  background-color: #434343;
  border-top: 2px solid #C1C1C1;
  border-right: 2px solid #C1C1C1;
  border-bottom: 2px solid #181818;
  border-left: 2px solid #181818;
  box-shadow: 0px 0px 2px #030303, inset 0px -20px 1px #2E2E2E;
}

.digits {
  color: #181818;
  text-shadow: 1px 1px 0px #FFF;
  background-color: #EBEBEB;
  border-top: 2px solid #FFF;
  border-right: 2px solid #FFF;
  border-bottom: 2px solid #C1C1C1;
  border-left: 2px solid #C1C1C1;
  border-radius: 4px;
  box-shadow: 0px 0px 2px #030303, inset 0px -20px 1px #DCDCDC;
}

.digits:hover,
.mathButtons:hover,
#clearButton:hover {
  background-color: #FFBA75;
  box-shadow: 0px 0px 2px #FFBA75, inset 0px -20px 1px #FF8000;
  border-top: 2px solid #FFF;
  border-right: 2px solid #FFF;
  border-bottom: 2px solid #AE5700;
  border-left: 2px solid #AE5700;
}

#clearButton {
  color: #FFF;
  text-shadow: -1px -1px 0px #44006F;
  background-color: #D20000;
  border-top: 2px solid #FF8484;
  border-right: 2px solid #FF8484;
  border-bottom: 2px solid #800000;
  border-left: 2px solid #800000;
  box-shadow: 0px 0px 2px #030303, inset 0px -20px 1px #B00000;
}
</style>