The green bar is an indicator of your browsers more secure https (SSL) certificate than yours. Such encryption is more expensive.
A different browser and / or color may be displayed in a different browser, and you cannot predict or set how it will look on your visitor computer. If your site is designed only to run on computers that you manage (for example, at a kiosk or exhibition or on the intranet), you can achieve your goal:
- full screen mode
- browser extensions
- Web application embedded in your application
- ...
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