Changing the background color of Markdown cells

[enmengliu]

Hi there,

I am developing a Jupyterlab extension and I want to highlight some of the cells by changing their background colors. My current way (attached below) works for code cells but does not work for Markdown cells. To be more specific, the background color of Markdown cells only changes after I double clicks on it to make it editable. I’m wondering whether there’s a way to highlight a Markdown cell without clicking on it?

My current way of highlighting code cells:

const highlightCell = (cellIndex: number) => {
      if (props.notebookTracker === null || props.notebookTracker.currentWidget === null) {
          console.log('[highlightCell] no notebookTracker or no notebookPanel.');
          return;
      }
     // get cell by cellIndex
      const cellList = props.notebookTracker.currentWidget.content.widgets;
      const cell = cellList[cellIndex];
      if (cell && cell.editor instanceof CodeMirrorEditor) {
          const editor = cell.editor.editor;
          const styleClass = "jp-InputArea-editor-dependencyline"; // background-color is defined in this class
          editor.addLineClass(0, "background", styleClass); // highlight the first line of that code cell
          console.log(`[highlightCell] highlighted the 1st line of the cell ${cellIndex}.`);
      }
      else {
          console.log('[highlightCell] the editor of activeCell is not a CodeMirrorEditor');
      }
  }

This works well for code cells:

but for Markdown cells, it requires double click to get the new background color showing.

Any help would be appreciated! Thank you in advance!