doccano/frontend/assets/style/editor.css

/* dark mode styles */
.theme--dark .tui-editor-contents h1 {
  color: #fff; /* inversion of #000 */
}

.theme--dark .tui-editor-contents h2,
.theme--dark .tui-editor-contents h3,
.theme--dark .tui-editor-contents h4,
.theme--dark .tui-editor-contents h5,
.theme--dark .tui-editor-contents h6,
.theme--dark .tui-editor-contents code span {
  color: #ccc; /* inversion of #333 */
}

.theme--dark .tui-editor-contents blockquote {
  color: #888; /* inversion of #777777 */
}

.theme--dark .tui-editor-contents ul,
.theme--dark .tui-editor-contents menu,
.theme--dark .tui-editor-contents ol,
.theme--dark .tui-editor-contents dir,
.theme--dark .tui-editor-contents p,
.theme--dark .tui-editor-contents table {
  color: #aaa; /* inversion of #555555 */
}

.theme--dark .tui-editor-contents table td {
  border: #151515; /* inversion of #eaeaea */
}

.theme--dark .tui-editor-contents table th {
  border: #8d8884; /* inversion of #72777b */
  background-color: #847e7b; /* inversion of #7b8184 */
}

.theme--dark .tui-editor-contents pre {
  background-color: #0a0807; /* inversion of #f5f7f8 */
}

.theme--dark .tui-editor-contents code {
  color: #3e8774; /* inversion of #c1788b */
}