LockDown Browser for Windows is compatible with "high contrast" settings (Windows 10) and "contrast themes" (Windows 11) set via the Windows operating system.
For Windows 10, the high contrast settings are made by navigating to "Settings" > "High Contrast"
You'll first want to turn on the high contrast setting, then you can adjust the colors to your preference.
After you make your desired changes, LockDown Browser will use those same settings.
For Windows 11, the "contrast themes" can be selected by navigating to "Settings" > "Accessibility" > "Contrast Themes." LockDown Browser will honor whatever theme you select.