常連

質問者さんのコードの文法的な誤りなどを修正したもので検証しましたが、問題が再現しませんでした。以下のコードを一度実行してみてください。
```HTML
<!DOCTYPE html>
<html lang="ja">
<head>
    <meta charset="UTF-8">
    <title>###</title>
    <link rel="icon" href="icon.jpg">
    <style type="text/css">
.tab-change a,table{background-color:#fff}.tab-change{height:auto;margin:10% 27% 15%}.tab-change a{border-radius:7px 7px 0 0;display:inline-block;line-height:38px;text-align:center;color:#000;margin-left:auto;margin-right:6%;font-size:20px;float:right;text-decoration:none;padding:0 32px}.Day-title,.Week-title{margin-left:10%;border-bottom:3px solid #23c1ea;margin-top:20%;text-align:center}.Day-title,.Week-title,table{font-size:25px}.tab-change a:hover{opacity:.6}.tab-change a:nth-child(1),.tab-change a:nth-child(2),.tab-change a:nth-child(3){border-top:6px solid #23c1ea}.content{height:320px;display:none}.box:after,.content:target{display:block}.Week-title{width:17%;padding-top:8%}.Day-title{width:24%;padding-top:8%}.day tr td,.week tr td,table{border:1px solid #000}table{margin-left:0;margin-right:auto;width:100%;height:100%}.day img,.week img{width:200px}.day,.week{text-align:center;font-size:22px;margin-top:auto;margin-left:10%;margin-right:10%}#explain-1,#explain-2{margin-left:47%;font-size:22px}.box:after{content:' ';clear:both}.base{position:relative}.low-frequency,.low-frequency2{position:absolute;left:-8%}.decibel{margin-top:0;padding-top:8%}.out{position:relative}.in{position:absolute}#explain-1::before,#explain-2::before{position:relative;top:.8em;margin-right:.5em}#explain-1{margin-top:10%;padding:0}#explain-1::before{content:url(https://placehold.jp/3d4070/ffffff/150x150.png?text=symbol-2.png)}#explain-2{margin-top:17%}#explain-3,.small-1{padding-right:55%;margin-left:13%}#explain-2::before{content:url(https://placehold.jp/3d4070/ffffff/150x150.png?text=symbol-1.png)}#explain-3{padding-top:10%;font-size:22px}.small-1{padding-top:0;margin-top:23%}.small-2{margin-left:16%}.explain{margin-right:5%;margin-left:10%;font-size:22px}.frequency-levels img{width:40%;height:40%;margin-top:-10%;margin-left:5%}.decibel-levels img{width:32%;height:32%;padding:0;margin:3% 50% 5% 10%}.howtosee-title,.howtosee-title2,.howtosee-title3{border-bottom:3px solid #23c1ea;font-size:26px;text-align:center;margin-left:10%}.howtosee-title{width:14%;padding-top:10%}.howtosee-title2{width:12%;padding-top:10%}.howtosee-title3{width:17%;margin-top:10%}
    </style>
</head>
<body>
<div class="main">
    <p class="photo-title">###</p>
    <div class="box">
        <div class="whole-photo">
            <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=pic.png">
        </div>
    </div>
    <div class="note" id="note">
        <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=green.png" class="tape"/>
        <p class="memo-title">〜メモ〜</p>
        <div class="letters">
            <p>"""
            </p>
        </div>
    </div>
    <div>
        <div>
            <nav class="tab-change">
                <a href='#howtosee'>見かた</a>
                <a href='#this-week'>一週間</a>
                <a href='#today'>今日</a>
            </nav>
        </div>
        <div id='today' class='content'>
            <p class="Day-title"><span id="view_today"></span>音情報</p>
            <div class="day">
                <table border="1" rules="cols">
                    <tr>
                        <td>10時</td>
                        <td>12時</td>
                        <td>14時</td>
                        <td>16時</td>
                        <td>18時</td>
                    </tr>
                    <tr>
                        <td>
                            <div class="base">
                                <div class="low-frequency">
                                    <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=frequency-4.png">
                                </div>
                                <div class="decibel">
                                    <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=decibel-2.png">
                                </div>
                            </div>
                            <p>79Hz</p>
                        </td>
                        <td>
                            <div class="base">
                                <div class="low-frequency">
                                    <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=frequency-1.png">
                                </div>
                                <div class="decibel">
                                    <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=decibel-2.png">
                                </div>
                            </div>
                            <p>237Hz</p>
                        </td>
                        <td>
                            <div class="base">
                                <div class="low-frequency">
                                    <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=frequency-3.png">
                                </div>
                                <div class="decibel">
                                    <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=decibel-3.png">
                                </div>
                            </div>
                            <p>195Hz</p>
                        </td>
                        <td>
                            <div class="base">
                                <div class="low-frequency">
                                    <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=lowest.png">
                                </div>
                                <div class="decibel">
                                    <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=decibel-2.png">
                                </div>
                            </div>
                            <p>250Hz</p>
                        </td>
                        <td>
                            <div class="base">
                                <div class="low-frequency">
                                    <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=frequency-3.png">
                                </div>
                                <div class="decibel">
                                    <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=decibel-3.png">
                                </div>
                            </div>
                            <p>129Hz</p>
                        </td>
                    </tr>
                </table>
            </div>
        </div>
        <div id='this-week' class='content'>
            <p class="Week-title">情報</p>
            <div class="week">
                <table border="1" rules="cols">
                    <tr>
                        <td>月</td>
                        <td>火</td>
                        <td>水</td>
                        <td>木</td>
                        <td>金</td>
                        <td class="hide">土</td>
                        <td class="hide">日</td>
                    </tr>
                    <tr>
                        <td>
                            <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=rest.png">
                        </td>
                        <td>
                            <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=rest.png">
                        </td>
                        <td>
                            <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=rest.png">
                        </td>
                        <td>
                            <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=rest.png">
                        </td>
                        <td>
                            <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=rest.png">
                        </td>
                        <td class="hide">
                            <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=rest.png">
                        </td>
                        <td class="hide">
                            <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=rest.png">
                        </td>
                    </tr>
                </table>
            </div>
        </div>
        <div id='howtosee' class='content'>
            <p class="howtosee-title">見方</p>
            <div class="out">
                <p class="in" id="explain-1">###</p>
            </div>
            <div class="frequency-levels">
                <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=frequency-levels.png">
            </div>
            <p class="small-1">####</p>
            <div class="out">
                <p class="in" id="explain-2">####</p>
            </div>
            <div class="decibel-levels">
                <img src="https://placehold.jp/3d4070/ffffff/150x150.png?text=decibel-levels.png">
            </div>
            <p id="explain-3">####</p>
            <p class="small-2">#####</p>
            <p class="howtosee-title2">###</p>
            <p class="explain">####</p>
            <p class="explain">
                <br>####。
                <br/>
                <br>#####
                <br/>
            </p>
            <p class="howtosee-title3">###</p>
            <p class="explain">###。
                <br>
                <br>###
            </p>
        </div>
        
    </div>
</div>
</body>
</html>


```
**動作確認済みブラウザ**
- Google Chrome(バージョン: `59.0.3071.115`)
- Firefox(バージョン: `54.0.1`)
- Opera(バージョン: `46.0.2597.26314`)

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