zammad/public/assets/form/form.css

.zammad-form {
  width: 100%;
}

.zammad-form h1, .zammad-form h2 {
  margin-top: 0;
}

.zammad-form .form-group {
  margin-bottom: 15px;
}

.zammad-form .form-control {
  display: block;
  width: 100%;
}

.zammad-form .has-error .form-control {
  border-color: #a94442;
}
.zammad-form .has-error label {
  color: #a94442;
}

.zammad-form .js-thankyou {
  text-align: center;
}

.zammad-form-modal {
    position: fixed;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    text-align: center;
    z-index: 999;
}

.zammad-form-modal:before {
    content: "";
    display: inline-block;
    height: 100%;
    vertical-align: middle;
    margin-right: -0.25em;
}

.zammad-form-modal-backdrop {
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    opacity: 0.7;
    background-color: gray;
}

.zammad-form-modal-body {
    text-align: left;
    background: white;
    border-radius: 5px;
    padding: 24px 24px 22px;
    width: 90%;
    max-width: 26em;
    margin: 0 auto;
    box-sizing: border-box;
    position: relative;
    display: inline-block;
    vertical-align: middle;
    box-shadow: 0 0 50px rgba(0,0,0,.3);
    color: #949494;
}