グリッドシステムの基本構造
.container
└ .row
├ .col
├ .col
└ .col
<div class="container">
<div class="row">
<div class="col-md-4">●●●</div>
<div class="col-md-4">●●●</div>
<div class="col-md-4">●●●</div>
</div>
</div>
—
.container
└ .row
├ .col
├ .col
└ .col
<div class="container">
<div class="row">
<div class="col-md-4">●●●</div>
<div class="col-md-4">●●●</div>
<div class="col-md-4">●●●</div>
</div>
</div>