jupyterlab/packages/debugger/style/editor.css

/*-----------------------------------------------------------------------------
| Copyright (c) Jupyter Development Team.
| Distributed under the terms of the Modified BSD License.
|----------------------------------------------------------------------------*/

.jp-DebuggerEditor-highlight {
  background-color: var(--jp-warn-color0);
}

.jp-DebuggerEditor-marker {
  position: absolute;
  left: -34px;
  top: -1px;
  color: var(--jp-error-color1);
}