Refine light theme contrast

[drdator]

Summary

• soften major, minor, and origin grid colors in the light theme
• make selected toolbar tools clearer with a tinted fill and darker amber treatment
• preserve CSS grid transparency in the WebGL 3D renderer
• leave dark and high-contrast theme styling unchanged

Verification

• npm run check (484 tests)
• visual verification in light and dark themes
• confirmed WebGL renders without errors