Unfortunately, the Safari graphics interface cannot be modified but try System Preferences > Accessibilty > Display and Zoom and try More Options.
Try inverting colors and using grayscale and contrast.
And a different screen resolution. System Preferences > Displays > Display
Select: Scaled
Try a different resolution.
You may have better luck using a different browser for vision impaired accessibility features.
Firefox offers more options > Accessibility features in Firefox - Make Firefox and web content work for all users | Firefox Help
Mozilla Firefox Web Browser — Free Download — mozilla.org