<link href="//netdna.bootstrapcdn.com/bootstrap/3.0.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//netdna.bootstrapcdn.com/bootstrap/3.0.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<h1>Pure CSS Connect 4</h1>
<form>
<div class="board">
<div class="field">
<div class="grid column">
<input type="radio" name="slot11" tabindex="-1" required>
<input type="radio" name="slot11" tabindex="-1" required>
<div class="disc"></div>
<input type="radio" name="slot12" tabindex="-1" required>
<input type="radio" name="slot12" tabindex="-1" required>
<div class="disc"></div>
<input type="radio" name="slot13" tabindex="-1" required>
<input type="radio" name="slot13" tabindex="-1" required>
<div class="disc"></div>
<input type="radio" name="slot14" tabindex="-1" required>
<input type="radio" name="slot14" tabindex="-1" required>
<div class="disc"></div>
<input type="radio" name="slot15" tabindex="-1" required>
<input type="radio" name="slot15" tabindex="-1" required>
<div class="disc"></div>
<input type="radio" name="slot16" tabindex="-1" required>
<input type="radio" name="slot16" tabindex="-1" required>
<div class="disc"></div>
<div class="column">
<input type="radio" name="slot21" tabindex="-1" required>
<input type="radio" name="slot21" tabindex="-1" required>
<div class="disc"></div>
<input type="radio" name="slot22" tabindex="-1" required>
<input type="radio" name="slot22" tabindex="-1" required>
<div class="disc"></div>