文本域（含边框）的宽度100%显示实例页面

CSS代码：

/*仅border是固定数值*/
.box { padding: 40px 0 40px 6px; background-color: #34538b;}
.box textarea {
    width: 99%;
    height: 80px;
    padding: 2px 0.5%;
    margin-left: -6px;
    border: 3px solid #cd0000;
    overflow: auto;
}
.box textarea:-moz-read-write {
    width: calc(100% - 6px);
    padding: 2px 3px;	
}

/* border, padding一起固定数值 */
.box2 { padding: 40px 0 40px 12px; background-color: #34538b; }
.box2 textarea {
    width: 100%;
    height: 80px;
    padding: 2px 3px;
    margin-left: -12px;
    border: 3px solid #cd0000;
    overflow: auto;
}
                

HTML代码：

<div class="box"><textarea></textarea></div>
<div class="box2"><textarea></textarea></div>