Order confirmation template: Red highlights and editing issues - Help needed

[Shopuser_2h1]

I'm working on customizing an order confirmation email template in Shopify. In the editor, I've noticed that certain parts of the code are highlighted in red, specifically:

The condition {% if line.quantity < line.quantity %}

The line <span class="order-list__item-title">{{ line_title }} × {{ line_display }}</span><br/>

The opening tags <span class="order-list__item-variant"> and <span class="order-list__item-refunded">

I can edit the code before the line containing {% if line.quantity < line.quantity %}, but I'm unable to add new code anywhere after. I've tried to do edits locally and add them, but I can delete the entire code in the editor.

What could be causing this, and how can I resolve it to make the necessary edits to my template?

Are these red highlights indicating specific errors I need to address?

Thanks!