Div error

index.html:
<!DOCTYPE html>
  <head>
    <title>Flexbox Layout Test</title>
    <link rel="stylesheet" href="style.css">
  </head>

  <body>
      <div class="gallery_head">
      <h2>Flexbox Gallery</h2>
      </div>


      <section class="gallery-links">
        <div class="wrapper">

        <div class="gallery-container">
          <a href="#">
            <div></div>
            <h3>Picture Title</h3>
            <p>Picture paragraph</p>
          </a>
        </div>
        <div class="gallery-container">
          <a href="#">
            <div></div>
            <h3>Picture Title</h3>
            <p>Picture paragraph</p>
          </a>
        </div>
        <div class="gallery-container">
          <a href="#">
            <div></div>
            <h3>Picture Title</h3>
            <p>Picture paragraph</p>
          </a>
        </div>
        <div class="gallery-container">
          <a href="#">
            <div></div>
            <h3>Picture Title</h3>
            <p>Picture paragraph</p>
          </a>
        </div>
        <div class="gallery-container">
          <a href="#">
            <div></div>
            <h3>Picture Title</h3>
            <p>Picture paragraph</p>
          </a>
        </div>
        <div class="gallery-container">
          <a href="#">
            <div></div>
            <h3>Picture Title</h3>
            <p>Picture paragraph</p>
          </a>
        </div>
        <div class="gallery-container">
          <a href="#">
            <div></div>
            <h3>Picture Title</h3>
            <p>Picture paragraph</p>
          </a>
        </div>
        <div class="gallery-container">
          <a href="#">
            <div></div>
            <h3>Picture Title</h3>
            <p>Picture paragraph</p>
          </a>
        </div>

      </div>

      </section>
  </body>

style:
* {
  margin: auto;
  padding: 0;
  border-radius: 15px;
  }

  body {
    background-color: black;
  }

  .gallery_head {
    background-color: white;
    text-align: center;
    width: 80%
  }

  .wrapper {
    width: 80%;
    Height: 100;
    background-color: white;

    display: flex;
    flex-wrap: wrap;
    flex-direction:row;
    /*flex-flow: row wrap;  <--  This contains both "flex-wrap: wrap" and "flex-direction:row"*/
    justify-content:space-between;
  }

  .gallery-container a div {
    width: 100%;
    height: 235px;
    background-color: lightgrey;
    background-position: center;
    background-repeat: no-repeat;
    background-size: cover;
  }

  /* Efectos tontos */
  .gallery-container a:hover {
      box-shadow: 0 0 4px rgba(0, 140, 186, 0.8);
  }
/* Fin efectos tontos */