Потрите `.flux-widget .chat-app .btn-default` у себя

button.css

.flux-widget .chat-app .btn-default {
  font-family: 'Roboto', sans-serif;
  position: relative;
  display: inline-block;
  box-sizing: border-box;
  margin: 0;
  background: transparent;
  color: rgba(0, 0, 0, .9);
  font-weight: 300;
  font-size: 16px;
  height: 40px;
  line-height: 20px;
  padding: 6px 20px;
  cursor: pointer;
  text-align: center;
  white-space: nowrap;
  border: 1px dashed rgba(0, 0, 0, .3);
  border-radius: 4px;
}
.flux-widget .chat-app .btn-default:focus {
  border: 1px solid rgba(0, 0, 0, .9);
  background: transparent;
  outline: 0;
  box-shadow: 0px 0px 0px 1px rgba(0, 0, 0, .9);
}

.flux-widget .chat-app .btn-default:hover {
  color: rgba(239, 49, 36, .9);
  border: 1px dashed rgba(239, 49, 36, .5);
  box-shadow: none;
}