Помогите не могу разобрать с Flex css и html не получаеться

.flex-container {
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  justify-content: center;
  align-items: flex-start;
  align-content: stretch;
}

.flex-items:nth-child(1) {
  display: block;
  flex-grow: 0;
  flex-shrink: 1;
  flex-basis: auto;
  align-self: auto;
  order: 0;
}

.flex-items:nth-child(2) {
  display: block;
  flex-grow: 0;
  flex-shrink: 1;
  flex-basis: auto;
  align-self: auto;
  order: 0;
}

.flex-items:nth-child(3) {
  display: block;
  flex-grow: 0;
  flex-shrink: 1;
  flex-basis: auto;
  align-self: auto;
  order: 0;
}

<div class="flex-container">
  <div class="flex-items">
    <img src="" class="card-img-top" alt="...">
    <div class="card-body">
      <h5 class="card-title">Card title</h5>
      <p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
      <a href="#" class="btn btn-primary">Go somewhere</a>
  </div>
  <div class="flex-items">
    <img src="" class="card-img-top" alt="...">
    <div class="card-body">
      <h5 class="card-title">Card title</h5>
      <p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
      <a href="#" class="btn btn-primary">Go somewhere</a>
  </div>
  <div class="flex-items">
    <img src="" class="card-img-top" alt="...">
    <div class="card-body">
      <h5 class="card-title">Card title</h5>
      <p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
      <a href="#" class="btn btn-primary">Go somewhere</a>
  </div>
</div>