Given the following CSS
.comment {
    margin: 10px;
    display: block;
    overflow: auto;
    border-top-left-radius: 5px 5px;
    border-top-right-radius: 5px 5px;
    border-bottom-right-radius: 5px 5px;
    border-bottom-left-radius: 5px 5px;
    -webkit-box-shadow: rgba(0, 0, 0, .2) 1px 1px 3px;
    -moz-border-radius: 5px;
    -webkit-border-radius: 5px;
    min-height: 200px;
    width: 100% 
}
This is applied to a textarea but the right margin is ignored and the textarea goes off the screen. 
why is this?