如何在Html / Bootstrap中控制容器的大小？

<div style="width: 300px; height: 200px;"></div>

<style>
    .container {
        width: 300px;
        height: 200px;
    }
</style>
<div class="container"></div>

.container {
    width: 300px;
    height: 200px;
}

<link rel="stylesheet" href="style.css">
<div class="container"></div>

<div class="container">
    <div class="row">
        <div class="col-lg-4 col-md-6 col-sm-12">内容</div>
        <div class="col-lg-4 col-md-6 col-sm-12">内容</div>
        <div class="col-lg-4 col-md-6 col-sm-12">内容</div>
    </div>
</div>