div.numberedtextarea-wrapper {
    position: relative;
}

    div.numberedtextarea-wrapper textarea {
        display: block;
        -webkit-box-sizing: border-box;
        -moz-box-sizing: border-box;
        box-sizing: border-box;
    }

div.numberedtextarea-line-numbers {
    position: absolute;
    display: none;
    background-color: #fafafa;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    width: 40px;
    border-right: 1px dashed #eee;
    border-bottom: solid 1px #ddd;
    color: #999;
    overflow: hidden;
}

div.numberedtextarea-number {
    padding-right: 6px;
    text-align: center;
}