<div class="container">
    <div class="header">header</div>
    <main class="grid">
        <div class="numbers">
            <div class="place"><div class="place__inner"><div class="place__content">1</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">2</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">3</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">4</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">5</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">6</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">7</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">8</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">9</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">10</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">11</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">12</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">13</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">14</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">15</div></div></div>
            <div class="place"><div class="place__inner"><div class="place__content">16</div></div></div>
        </div>
    </main>
    <div class="footer">footer</div>
</div>

* {
    font-family: sans-serif;
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}

.container {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.header {
    height: 60px;
    background: #0D0;
}

.footer {
    height: 60px;
    background: #D00;
}

.grid {
    width: 100%;
    max-width: 700px;
    margin: 0 auto;
    padding: 0 15px;
    
    flex-grow: 1;
    display: flex;
    justify-content: center;
    align-items: center;
}

.numbers {
    margin: 0 auto;

    flex-grow: 1;
    display: flex;
    flex-wrap: wrap;
}

.place {
    flex: 0 1 calc(100% / 4 - 10px);
    margin: 5px;
    background: #DDD;
}

.place__inner {
    position: relative;
    
    height: 0;
    padding-bottom: 100%;
}

.place__content {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;

    display: flex;
    justify-content: center;
    align-items: center;
}