(1)使用float

<div class="use-float">
    <div></div>
    <div></div>
</div>
.use-float>div:first-child{
    width:100px;
    float:left;
}
.use-float>div:last-child{
    overflow:hidden;
}

(2)使用table

<table class="use-table">
    <tr>
        <td></td>
        <td></td>
    </tr>    
</table>
.use-table{
    border-collapse:collapse;
    width:100%;
}
.use-table>tbody>tr>td:first-child{
    width:100px;
}

(3)用div模拟table

<div class="use-mock-table">
    <div></div>
    <div></div>
</div>
.use-mock-table{
    display:table;
    width:100%;
}
.use-mock-table>div{
    display:table-cell;
}
.use-mock-table>div:first-child{
    width:100px;
}

(4)使用flex

<div class="use-flex">
    <div></div>
    <div></div>
</div>
.use-flex{
    display:flex;
}
.use-flex>div:first-child{
    flex:none;
    width:100px;
}
.use-flex>div:last-child{
    flex:1;
}

效果图:
左边div固定宽度,右边div自适应