Untitled

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Calculator</title>
    <link rel="stylesheet" href="node_modules/bootstrap/dist/css/bootstrap.css">
    <link rel="stylesheet" href="css/master.css">
</head>
<body>
    <div style="margin: auto;width: 400px;" class="container">
        <div class="row">
            <div class="col-xs-9">
                <input type="text" class="form-control" readonly>
            </div>
            <div class="col-xs-3">
                <button type="button" class="btn btn-danger btn-block">C</button>
            </div>
        </div>
        <div class="row">
            <div class="col-xs-3">
                <button type="button" class="btn btn-default btn-block">7</button>
            </div>
            <div class="col-xs-3">
                <button type="button" class="btn btn-default btn-block">8</button>
            </div>
            <div class="col-xs-3">
                <button type="button" class="btn btn-default btn-block">9</button>
            </div>
            <div class="col-xs-3">
                <button type="button" class="btn btn-danger btn-block">/</button>
            </div>
        </div>
        <div class="row">
            <div class="col-xs-3">
                <button type="button" class="btn btn-default btn-block">4</button>
            </div>
            <div class="col-xs-3">
                <button type="button" class="btn btn-default btn-block">5</button>
            </div>
            <div class="col-xs-3">
                <button type="button" class="btn btn-default btn-block">6</button>
            </div>
            <div class="col-xs-3">
                <button type="button" class="btn btn-danger btn-block">*</button>
            </div>
        </div>
        <div class="row">
            <div class="col-xs-3">
                <button type="button" class="btn btn-default btn-block">1</button>
            </div>
            <div class="col-xs-3">
                <button type="button" class="btn btn-default btn-block">2</button>
            </div>
            <div class="col-xs-3">
                <button type="button" class="btn btn-default btn-block">3</button>
            </div>
            <div class="col-xs-3">
                <button type="button" class="btn btn-danger btn-block">-</button>
            </div>
        </div>
        <div class="row">
            <div class="col-xs-3 col-xs-offset-3">
                <button type="button" class="btn btn-default btn-block">0</button>
            </div>
            <div class="col-xs-3">
                <button type="button" class="btn btn-default btn-block">=</button>
            </div>
            <div class="col-xs-3">
                <button type="button" class="btn btn-danger btn-block">+</button>
            </div>
        </div>
    </div>
</body>
</html>