body {
  background: #fff;
}

h1, h2 {
    text-align: center;
    font-family: Verdana, sans-serif;
}

td {
    text-align: center;
}

input[type="text"] {
    height: 25px;
    font-size: 20px;
}

#background {
    width:600px;
    height:200px;
    background:gray;
    margin:50px auto;
    padding: 0;
}

button {
    border:0;
    color:#fff;
}

.result {
    font-family: sans-serif;
    width: 230px;
    height: 40px;
    text-align: center;
    border: 0;
    background: #3b3535;
    color: #fff;
    padding-top: 0;
    font-size: 20px;
    outline: none;
    overflow: hidden;
    letter-spacing: 4px;
    padding: 4px 4px 8px 4px;
}

#result:hover {
    cursor: text;
}

/* Button styling */
.btn-style {
    width:125px;
    height:50px;
    margin-left:5px;
    border-radius:4px;
    margin-bottom: 10px;
}

/* Adding background color to the number values */
 .num-bg {
    background:#000;
    color:#fff;
    font-size:26px;
    cursor:pointer;
    outline:none;
    border-bottom:3px solid #333;
}

 .num-bg:active {
    background:#000;
    color:#fff;
    font-size:26px;
    cursor:pointer;
    outline:none;
    box-shadow: inset 5px 5px 5px #555;
}