SOURCE

<div style="width: 700px; height: 400px; background: red; position:absolute">



    <div class="grid-container">
        <div>
            <div>123123</div>
        </div>
        <div>2</div>
        <div>3</div>
        <div>4</div>
        <div>5</div>
        <div>6</div>
        <div>7</div>
        <div>8</div>
        <div>9</div>
    </div>

</div>

.grid-container{
    padding-bottom: 100%;
  display: grid;
  /* grid-template-columns: 100px 100px 100px; */
   grid-template-columns: repeat(auto-fill, 33%); 
  grid-template-rows: repeat(auto-fill, 33%);
  /* height: 100%; */
  background: #d4d4d4;
}
.grid-container > div {
  border: 1px grey solid;
  padding-bottom: 100%;
}
html,body{
  height: 100%;
  width: 100%;
}