Currently, only List layout has the correct implementation:

• Gray background on placeholders.
• 1px semi-transparent border (to ensure the image boundaries are always visible).

The following need to be addressed:

• Pages – Grid layout: gray background is missing on placeholders.
• Pages – Table layout: placeholder is missing entirely. Border is missing.
• Patterns – border is missing. Fixed in Update Grid layout design #57880

Ideally this would be implemented in a way that is easy for third parties to replicate.