<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            box-sizing: border-box;
            padding: 0;
            margin: 0;
        }

        body{
            background-color: grey;
        }
        .grid {
            display: grid;
            grid-template-columns: repeat(4, 1fr);
            grid-auto-rows: 150px;
            background-color: black;
            width: 600px;
            outline: 1px solid black;
            margin: 150px auto;
        }

        .elem {
            height: 100%;
            width: 100%;
            display: flex;
            align-items: center;
            justify-content: center;
            font-weight: bold;
            font-size: 18px;
            color: #fff;
            position: relative;

            &:before {
                content: '';
                position: absolute;
                top: 0;
                left: 0;
                mask: url("data:image/svg+xml;charset=UTF-8,%3csvg width='100' height='100' viewBox='0 0 100 100' fill='none' xmlns='http://www.w3.org/2000/svg'%3e%3cpath fill-rule='evenodd' d='M0 0H100V100H0V0ZM14 4H86C91.5229 4 96 8.47715 96 14V86C96 91.5229 91.5229 96 86 96H14C8.47715 96 4 91.5229 4 86V14C4 8.47715 8.47715 4 14 4Z' fill='white'/%3e%3c/svg%3e");
                mask-repeat: no-repeat;
                mask-size: cover;
                background-color: white;
                height: 100%;
                width: 100%;
            }
        }
    </style>
</head>

<body>

    <div class="grid">
        <div class="elem">
            1
        </div>
        <div class="elem">2</div>
        <div class="elem"></div>
        <div class="elem"></div>
        <div class="elem"></div>
        <div class="elem"></div>
        <div class="elem"></div>
        <div class="elem"></div>
        <div class="elem"></div>
        <div class="elem"></div>
        <div class="elem"></div>
        <div class="elem"></div>
    </div>
</body>

</html>

External CSS

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External JavaScript

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