CSS - lineas horizontales y verticales de la GRID CSS

<style>

.grid-container {

  display: inline-grid;

  grid-template-columns: auto auto auto;

}

.grid-container>div {

    border: 1px solid #f00;

    padding: 20px;

    font-size: 30px;

    text-align: center;

}

</style>

<div class="grid-container">

  <div>1</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>