Tic Tac Toe 2 players in HTML , CSS , JS

<html>
<head>
<title>Tic Tac Toe</title>
<style>
input[type="button"]
{height:100px;
width:100px;
margin:5px 5px 5px 5px;
background-color:#FFFFAA;
color: black;
border: 2px solid #4CAF50;
transition-duration: 0.5s;
cursor: pointer;
border-radius:5px;
font-size: 50px;}
input[type="button"]:hover {background-color: #4CAF50;
color: white;
border: 2px solid #000000;}
#play {display:none;
height:500px;
width:400px;
position:absolute;
top:25%;
left:25%;
text-align:center;
box-shadow:0px 0px 10px #000000;
background-color:#B8EEF8;}
#start {position:absolute;
height:500px;
width:400px;
top:25%;
left:25%;
text-align:center;
box-shadow:0px 0px 10px #000000;
background-color:#B8EEF8;}
#go0 {height:50px;
width:200px;
margin:100px 10px 10px 10px;
background-color:#FFFFAA;
color: black;
border: 2px solid #4CAF50;
transition-duration: 0.5s;
cursor: pointer;
border-radius:25px;}
#go0:hover {background-color: #4CAF50;
color: white;
border: 2px solid #000000;}
#back0 {height:50px;
width:200px;
margin:20px 10px 40px 10px;
background-color:#FFFFAA;
color: black;
border: 2px solid #4CAF50;
transition-duration: 0.5s;
cursor: pointer;
border-radius:25px;}
#back0:hover {background-color: #4CAF50;
color: white;
border: 2px solid #000000;}
#p1 {margin:25px 10px 0px 10px;
font-size: 20px;}
#p2 {margin:0px 10px 0px 10px;}
</style>
<script>
var turn=0;
function done(x){if(turn==0){document.getElementById(x).disabled=true;
turn=1;
document.getElementById(x).value="X";}
else if(turn==1){document.getElementById(x).disabled=true;
turn=0;
document.getElementById(x).value="O";}}
function go(){document.getElementById("play").style.display = "block";
document.getElementById("start").style.display = "none";}
function back(){document.getElementById("start").style.display = "block";
document.getElementById("play").style.display = "none";}
</script>
</head>
<body>
<div id="start">
<p id="p1"><b>Tic Tac Toe</b></p><br/>
<p id="p2">2 Players</p><br/>
<button onclick="go()" id="go0">Start</button>
</div>
<div id="play">
<button onclick="back()" id="back0">Back</button>
<table align="center">
<tr>
<td><input type="button" value="" onclick="done('b1')" id="b1"/></td>
<td><input type="button" value="" onclick="done('b2')" id="b2"/></td>
<td><input type="button" value="" onclick="done('b3')" id="b3"/></td>
</tr>
<tr>
<td><input type="button" value="" onclick="done('b4')" id="b4"/></td>
<td><input type="button" value="" onclick="done('b5')" id="b5"/></td>
<td><input type="button" value="" onclick="done('b6')" id="b6"/></td>
</tr>
<tr>
<td><input type="button" value="" onclick="done('b7')" id="b7"/></td>
<td><input type="button" value="" onclick="done('b8')" id="b8"/></td>
<td><input type="button" value="" onclick="done('b9')" id="b9"/></td>
</tr>
</table>
</div>
</body>
</html>