<div id="section3" class="container">
<div class="big box">お問い合わせは<span class="nowrap">こちらから</span></div>
<div class="middle box">お問い合わせは<span class="nowrap">こちらから</span></div>
<div class="small box">お問い合わせは<span class="nowrap">こちらから</span></div>
</div>
body { font-size: 18px; line-height: 1.3; }
.container { padding: 3em; }
.container:after { clear: left; content: ""; display: block; }
.box { background: #fff; border: #d8d8d8 1px solid; box-sizing: border-box; float: left; margin-bottom: 20px; padding: 1em; text-align: center; }
.big { width: 300px; margin-right: 20px; }
.middle { width: 200px; margin-right: 20px; }
.small { width: 80px; }
.nowrap { white-space: nowrap; }