@stream-io/stream-chat-css/dist/scss/SendButton.scss

.str-chat__send-button {
  margin-left: var(--xs-m);
  border: 0;
  background: 0;
  outline: 0;

  &:focus {
    outline: 5px auto -webkit-focus-ring-color;
  }

  @media screen and (min-width: 768px) {
    display: none;
  }

  .str-chat__send-button-angular {
    svg path {
      fill: var(--primary-color);
    }
  }
}