Misafir adlı üyeden alıntı: mesajı görüntüle 
<!DOCTYPE html>
<html lang="tr">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }
        .zfc{
            width: 100%;
        }
        .zfc-item{
            width: calc(20% - 10px);
            margin-top: 20px;
            margin-left: 10px;
            height: 400px;
            float: left;
            background-color: red;
        }
        @media screen and (max-width:1000px) {
            .zfc-item{
                width: calc(50% - 10px);
            }
        }
    </style>
</head>
<body>
    



<div class="zfc">
    <div class="zfc-item"></div>
    <div class="zfc-item"></div>
    <div class="zfc-item"></div>
    <div class="zfc-item"></div>
    <div class="zfc-item"></div>
    <div class="zfc-item"></div>
    <div class="zfc-item"></div>
    <div class="zfc-item"></div>
    <div class="zfc-item"></div>
    <div class="zfc-item"></div>
    <div class="zfc-item"></div>
    <div class="zfc-item"></div>
    <div style="clear: both;"></div>
</div>


</body>
</html>

tam olarak anlamadım acaba attığınız kodu