Whenever you edit an icon and see a Code block appear, it's because the image has been installed as an SVG (Scalable Vector Graphic).
SVG images are razor sharp on higher resolution displays (i.e. retina).
Squarespace doesn't support (yet) installing SVG images via the standard image insert tools (Galleries or Inline Images) so we use the code block.
Most SVG code elements are added between a "div" code snippet:
This is used to center the image/icon. If you're adding a new SVG, just add within div. If replacing an existing SVG, just past over the entire SVG between the the div opening and closing tags.
SVG Standard Sizing
200x200 art board / canvas with a little padding