dify/web/app/components/base/checkbox/index.module.css

.mixed {
  background: var(--color-components-checkbox-bg) url(./assets/mixed.svg) center center no-repeat;
  background-size: 12px 12px;
  border: none;
}

.checked.disabled {
  background-color: #d0d5dd;
  border-color: #d0d5dd;
}