Button: scale default icon visuals to balance with small button labels #8620

Feature request

Consider adjusting the default size of standard Octicons in small buttons to preserve the perceived visual balance between the icon and label found in medium buttons.

Motivation

Small buttons reduce the label size but retain the same default 16px icon size as medium buttons, making the icon proportionally more prominent.

It would be helpful for the small variant to use an appropriate smaller default icon size, rather than requiring consumers to customize each visual. The goal is consistent perceived balance, not necessarily exact mathematical scaling, since icon crispness and supported Octicon sizes should inform the decision.

Proposed behavior

• Apply size-aware defaults to standard Octicons in both leading and trailing visuals.
• Preserve explicitly supplied icon sizes and custom visuals.
• Keep the existing medium button appearance unchanged.

The specific smaller icon size would need design exploration. Because this affects Button's visual proportions, the sizing decision may also need coordination across Primer implementations rather than being React-only.