message: fix scrollable window height
diff: line-height: 42px;
  opacity: 0;
  transition: opacity 0.5s, top 0.5s;
  + background-image: linear-gradient(#c1c1c1, transparent);
  &.jsxc_show {
  top: 0;
  }
  &.jsxc_mam-enable {
  - .jsxc_textarea {
  - padding-top: 42px;
  - }
  -
  .jsxc_mam-load-more {
  display: block;
  }
  