的外れかもしれませんが、以下のように記述するとどうでしょうか?
HTML
1<!DOCTYPE html>
2<html lang="ja">
3<head>
4 <meta charset="UTF-8">
5 <meta name="viewport" content="width=device-width, initial-scale=1.0">
6 <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/materialize/0.98.2/css/materialize.min.css">
7 <title>タイトル</title>
8 <style type="text/css">
9 @media screen and (max-width: 479px) {
10 .container, .container .row {
11 width: 100%;
12 margin-left: 0;
13 margin-right: 0;
14 }
15
16 .row .col {
17 padding: 0;
18 }
19 }
20
21 .grid-example {
22 border: 1px solid #eee;
23 margin: 7px 0;
24 text-align: center;
25 line-height: 50px;
26 font-size: 28px;
27 background-color: tomato;
28 color: white;
29 padding: 0;
30 }
31 </style>
32</head>
33<body>
34<div class="container">
35 <div class="row">
36 <div class="col s1 grid-example">
37 <span class="flow-text">1</span>
38 </div>
39 <div class="col s1 grid-example">
40 <span class="flow-text">2</span>
41 </div>
42 <div class="col s1 grid-example">
43 <span class="flow-text">3</span>
44 </div>
45 <div class="col s1 grid-example">
46 <span class="flow-text">4</span>
47 </div>
48 <div class="col s1 grid-example">
49 <span class="flow-text">5</span>
50 </div>
51 <div class="col s1 grid-example">
52 <span class="flow-text">6</span>
53 </div>
54 <div class="col s1 grid-example">
55 <span class="flow-text">7</span>
56 </div>
57 <div class="col s1 grid-example">
58 <span class="flow-text">8</span>
59 </div>
60 <div class="col s1 grid-example">
61 <span class="flow-text">9</span>
62 </div>
63 <div class="col s1 grid-example">
64 <span class="flow-text">10</span>
65 </div>
66 <div class="col s1 grid-example">
67 <span class="flow-text">11</span>
68 </div>
69 <div class="col s1 grid-example">
70 <span class="flow-text">12</span>
71 </div>
72 </div>
73</div>
74<script src="https://code.jquery.com/jquery-3.2.1.min.js"></script>
75<script src="https://cdnjs.cloudflare.com/ajax/libs/materialize/0.98.2/js/materialize.min.js"></script>
76</body>
77</html>