Alternating line-by-line background colors

I’d like to create a stylesheet that alternates background color on a line-by-line basis, e.g., white and light-green, similar to what you’d find on a traditional columnar accounting pad to make line differentiation visually easier.

How would I do this, assuming it is possible? Perhaps a script?

Thank you.

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I don’t think it’s possible without a script. With a script you can get started, though I’m not sure you’ll arive at a satisfactory solution. Here’s a quick start:

function EvenOddLineMarkerTaskPaperContextScript(editor, options) {
  function markEvenOddLines() {
    let items = editor.displayedItems
    for (var i = 0; i < items.length; i++) {
      let item = items[i]
	  let mark = i % 2 ? 'odd' : 'even'
      item.setAttribute('line', mark)

  editor.outline.onDidChange(function(mutation) {
    setTimeout(markEvenOddLines, 0)

  script: EvenOddLineMarkerTaskPaperContextScript.toString()

If you run that script it will mark all lines in the frontmost editor with line=odd or line=even attributes. It will also setup an event handler to remark all editor lines anytime the outline model changes. You can then style based on those attributes like this:

item[line=even] {
  background-color: red;
item[line=odd] {
  background-color: green;

It’s a start! Drawbacks include:

  1. I think it will slow down typing in longer documents
  2. The script is using some private “undoManger” API … could change in future, though I wouldn’t expect this particular bit to change.
  3. Script only updates when content changes, if you just fold / focus the lines won’t be colored. Possible to fix with more private API, but if you really want. Let me know.