textarea { background: #c0c0c0; border: 1px solid #888; width: 350px; height: 150px; }

textarea.linenumbers { resize: none; position: relative; left: 30px; }
.linenumbers-gutter { background-color: #f0f0f0; border-color: transparent;}
.linenumbers-gutter span { display: block; }
.linenumbers-gutter span.current-line { color: blue; }
.linenumbers-gutter span.success { background-color:lightgreen; }
.linenumbers-gutter span.warning { background-color:goldenrod; }
.linenumbers-gutter span.error { background-color:orangered; }