css-test-3

HTML:

    <div class="box-container">
        <div class="box">Box 1</div>
        <div class="box">Box 2</div>
        <div class="box">Box 3</div>
        <div class="box">Box 4</div>
    </div>

CSS:

.box-container {

}

.box {
  width: 100px;
  height: 100px;
  background-color: #ddd;
  color: #000;
  line-height: 100px;
}

Solution:

.box-container {
  display: flex;
  justify-content: center;
  align-items: center;
}