style.css

/* 
    CSS Style for grid from: GCyrillus. (2014, May 6). How to make a sudoku grid usin HTML and CSS [Answer 1]. Message posted to http://www.stackoverflow.com/questions/23497444/how-to-make-a-sudoku-grid-using-html-and-css
 */

#grid {
    margin:1em auto;
}
.cell {
    height:30px;
    width:30px;
    border:1px solid;
    text-align:center;
}
.cell input {
    width:30px;
    height:30px;
    font-size: 15px;
    text-align: center;
}
.cell:first-child {
    border-left:solid;
}
.cell:nth-child(3n) {
    border-right:solid ;
}
.row:first-child {
    border-top:solid;
}
.row:nth-child(3n) td {
    border-bottom:solid ;
}

body {
    text-align:center;
    min-width:600px;
}

.optionbuttons {
    margin: 0 auto;
    width: 300px;
    display: block;
    height: 30px;
    background-color: lightgray;
    font-size: 12px;
    margin-bottom: 5px;
}

#outputlist {
    padding:10px;
    text-align:center;
    list-style: none;
    width:300px;
    height:150px;
    background-color:#d9d9d9;
    display:block;
    margin: 20px auto;
}