Second axes breaks Firefox B&W printing

[hyunbinseo]

When printing the column examples on the following environment,

• OS: macOS 14.2.1
• Firefox: 121.0.1
• Destination: Samsung M203x Series
• Color mode: Black and white (disabled)
• Options: ✅ Print backgrounds

the ones with the second axes enabled are printed with a black background.

Expectation	Reality

Probably related to how the axes are implemented.

background-image: linear-gradient(0deg,var(--secondary-axes-color) var(--secondary-axes-width),transparent var(--secondary-axes-width));

Have not found a workaround yet.