spee.ch/client/scss/dropzone/_dropzone.scss

.dropzone-wrapper {
  // fill the parent flex container
  flex: 1 0 auto;
  // be a flex container for children
  display: flex;
  flex-direction: column;
}

.dropzone {
  border: 2px dashed #9b9b9b;
  // fill the parent flex container
  flex: 1 0 auto;
  // be a flex container for children
  display: flex;
  -webkit-flex-direction: column;
  flex-direction: column;
  justify-content: center;
  align-items: center;
}

.dropzone:hover, .dropzone--active {
  border: 2px dashed #4156C5;
  cursor: pointer;
}

.dropzone-dropit-display, .dropzone-instructions-display {
  padding: 1em;
  text-align: center;
}

.dropzone-preview-wrapper {
  position: relative;
  width: 100%;
  .dropzone-preview-overlay {
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    display: flex;
    -webkit-flex-direction: column;
    flex-direction: column;
    justify-content: center;
  }
}

.dropzone-preview-image {
  display: block;
  padding: 1em;
  width: calc(100% - 2em);
}