Examples of six CSS three-column layout methods

<style>
    .tree-columns-layout.float .left {
        float: left;
        width: 300px;
        background-color: #a00;
    }

    .tree-columns-layout.float .right {
        float: right;
        width: 300px;
        background-color: #0aa;
    }

    .tree-columns-layout.float .center {
        /* left: 300px;
        right: 300px; */
        margin: 0 300px;
        background-color: #aa0;
        overflow: auto;
    }
</style>
<section class="tree-columns-layout float">
    <article class="left">
        <h1>我是浮动布局左框</h1>
    </article>
    <article class="right">
        <h1>我是浮动布局右框</h1>            
    </article>
    <article class="center">
        <h1>我是浮动布局中间框</h1>            
    </article>
</section>

<style>
    .tree-columns-layout.position {
        position: relative;
    }

    .tree-columns-layout.position .left {
        position: absolute;
        left: 0;
        top: 0;
        width: 300px;
        background-color: #a00;
    }

    .tree-columns-layout.position .right {
        position: absolute;
        right: 0;
        top: 0;
        width: 300px;
        background-color: #0aa;
    }

    .tree-columns-layout.position .center {
        margin: 0 300px;
        background-color: #aa0;
        overflow: auto;
    }
</style>
<section class="tree-columns-layout position">
    <article class="left">
        <h1>我是浮动定位左框</h1>
    </article>
    <article class="center">
        <h1>我是浮动定位中间框</h1>
    </article>
    <article class="right">
        <h1>我是浮动定位右框</h1>
    </article>        
</section>

<style>
    .tree-columns-layout.table {
        display: table;
        width: 100%;
    }

    .tree-columns-layout.table > article {
        display: table-cell;
    }

    .tree-columns-layout.table .left {            
        width: 300px;
        background-color: #a00;
    }

    .tree-columns-layout.table .center {
        background-color: #aa0;
    }

    .tree-columns-layout.table .right {
        width: 300px;
        background-color: #0aa;
    }   
    
</style>
<section class="tree-columns-layout table">
    <article class="left">
        <h1>我是表格布局左框</h1>
    </article>
    <article class="center">
        <h1>我是表格布局中间框</h1>
    </article>
    <article class="right">
        <h1>我是表格布局右框</h1>
    </article>
</section>

<style>
    .tree-columns-layout.flex {
        display: flex;
    }    
    
    .tree-columns-layout.flex .left {
        width: 300px;
        flex-shrink: 0; /* 不缩小 */
        background-color: #a00;
    }

    .tree-columns-layout.flex .center {
        flex-grow: 1; /* 增大 */
        background-color: #aa0;
    }

    .tree-columns-layout.flex .right {
        flex-shrink: 0; /* 不缩小 */
        width: 300px;
        background-color: #0aa;
    }
</style>
<section class="tree-columns-layout flex">
    <article class="left">
        <h1>我是flex弹性布局左框</h1>
    </article>
    <article class="center">
        <h1>我是flex弹性布局中间框</h1>
    </article>
    <article class="right">
        <h1>我是flex弹性布局右框</h1>
    </article>
</section>

<style>
    .tree-columns-layout.grid {
        display: grid;
        grid-template-columns: 300px 1fr 300px;
    }

    .tree-columns-layout.grid .left {
        background-color: #a00;
    }

    .tree-columns-layout.grid .center {
        background-color: #aa0;
    }

    .tree-columns-layout.grid .right {
        background-color: #0aa;
    }
</style>
<section class="tree-columns-layout grid">
    <article class="left">
        <h1>我是grid栅格布局左框</h1>
    </article>
    <article class="center">
        <h1>我是grid栅格布局中间框</h1>
    </article>
    <article class="right">
        <h1>我是grid栅格布局右框</h1>
    </article>
</section>

<style>       
    .tree-columns-layout.cup:after {
        clear: both;
        content: "";
        display: table;
    }

    .tree-columns-layout.cup .center {
        width: 100%;
        float: left;            
    }

    .tree-columns-layout.cup .center > p {
        margin: 0 300px;
        overflow: auto;
        background-color: #aa0;
    }

    .tree-columns-layout.cup .left {
        width: 300px;
        float: left;
        margin-left: -100%;
        background-color: #a00;
    }

    .tree-columns-layout.cup .right {
        width: 300px;
        float: left;
        margin-left: -300px;
        background-color: #0aa;
    }
</style>
<section class="tree-columns-layout cup">
    <article class="center">
        <p>
            <h1>我是圣杯布局中间框</h1>
        </p>
    </article>
    <article class="left">
        <h1>我是圣杯布局左框</h1>
    </article>        
    <article class="right">
        <h1>我是圣杯布局右框</h1>
    </article>        
</section>