html {
   min-height: 100%;
   background-size: cover;
   background-repeat: no-repeat;
   background-position: center center;
}

.center-screen {
    display: flex;
    justify-content: center;
    align-items: center;
    text-align: center;
    min-height: 40vh;
    width: 100%;
    #background-color: #fff;
    #opacity: .5;
  }
  .wrapper {
    width: 100%;
    float: left;
    justify-content: center;
    align-items: center;
    display: flex;
    flex-direction: column;
    font-size: xxx-large;
  }
  img {
    width: 100%;
    max-width: 9vw;
    height: auto;
    background-color: #fff;
    opacity: .5;
  }
  .collapsible {
    background-color: #777;
    color: white;
    cursor: pointer;
    padding: 10px;
    width: 100%;
    border: none;
    text-align: left;
    outline: none;
    font-size: 15px;
  }
  
  .active, .collapsible:hover {
    background-color: #555;
  }
  
  .content {
    padding: 0 18px;
    display: none;
    overflow: hidden;
    background-color: #fff;
    opacity: .5;
  }