contenteditable 属性

<element contenteditable="value">

/**宽度固定，自动换行，内容超出滚动条显示***/
.divOne {
    width: 300px;
    height: 200px;
    border: 1px solid rgb(0,0,0);
    margin: 20px;
    overflow: hidden;
    overflow-y: auto;
    word-break: break-all;
    word-wrap: break-word;
    line-height: 20px;
    background: none;
}

    .divOne p {
        margin: 0px;
        padding: 0px;
    }

    .divOne:focus {
        border: 1px solid red;
        box-shadow: 0px 0px 30px rgba(0,255,0,0.5);
    }

/*宽度固定，高度自适应*/
.divTwo {
    width: 300px;
    height: auto;
    border: 1px solid blue;
    margin: 20px;
    overflow: hidden;
    word-break: break-all;
    word-wrap: break-word;
    line-height: 20px;
    background: none;
}

    <div class="divOne" contenteditable="true">
    </div>

    <div class="divTwo" contenteditable="true">
        <input type="button" value="按钮" />
    </div>