const editor = vscode.window.activeTextEditor;
        const doc = editor.document;

        // Set up ::before at the start and end of line 0
        const beforeDeco = vscode.window.createTextEditorDecorationType({
            before: {
                contentText: 'b',
                color: 'yellow'
            }
        });
        const line0Range = doc.lineAt(0).range;
        const line0Start = new vscode.Range(line0Range.start, line0Range.start);
        const line0End = new vscode.Range(line0Range.end, line0Range.end);
        editor.setDecorations(beforeDeco, [line0Start, line0End]);

        // Set up ::after at the start and end of line 1
        const afterDeco = vscode.window.createTextEditorDecorationType({
            after: {
                contentText: 'a',
                color: 'red'
            }
        });
        const line1Range = doc.lineAt(1).range;
        const line1Start = new vscode.Range(line1Range.start, line1Range.start);
        const line1End = new vscode.Range(line1Range.end, line1Range.end);
        editor.setDecorations(afterDeco, [line1Start, line1End]);

        // Set up ::before and ::after on line 3 (empty line)
        const beforeAfterDeco = vscode.window.createTextEditorDecorationType({
            before: {
                contentText: 'b',
                color: 'yellow'
            },
            after: {
                contentText: 'a',
                color: 'red'
            }
        });
        const line3Range = doc.lineAt(3).range;
        const line3Start = new vscode.Range(line3Range.start, line3Range.start);
        editor.setDecorations(beforeAfterDeco, [line3Start]);