mastodon/app/javascript/styles/mastodon/_custom.scss

.custom-img img {
  width: 100%;
  max-width: 50vw;
  display: block;
  margin: 0 auto;
}

.custom_message_heading {
  font-size: 2em;
  margin-bottom: 0.5em;
  text-align: center;
}
.page-show{
  min-height: 100vh;
  position: relative;
  top: 0;
  width: 100%;
  background: url('../images/home.jpg') no-repeat fixed center;
  background-size: cover;
}
.auth-page {
  min-height: 100vh;
  position: absolute;
  top: 0;
  width: 100%;
  background: url('../images/bliss/auth_background.jpg') no-repeat fixed center;
  background-size: cover;

  .form-container {
    background: rgba(0, 0, 0, 0.5);
  }

  .logo-container {
    width: 200px;
  }

  .img-custom {
    text-align: center;
    width: 440px;
    background: rgba(0, 0, 0, 0.5);
    margin: 0 auto;
    display: block;

    img {
      width: 400px;
      max-width: 90vw;
      margin: 1em auto;
      display: inline-block;
      border: solid 2px #111;
    }
  }

  .title {

    padding: 1em;
    font-size: 3em;
    margin-bottom: 0.5em;
  }
}