sRGB is the standard for Internet-based systems.
The color values provided by the web browser are then sent to the operating system.
From there, any color profile in use is read and then applied by the graphics card, so the values are then sent to the monitor.
This does not mean that you will get the same color on different scenarios.
There are different vendors, different quality controls, etc. sRGB is meant to be a generic standard.
Colors might be different even on the same monitor on the same computer. Calibration is needed to update the color profiles accordingly to the viewing conditions. Even the calibration tools need to be calibrated.
But that is another issue. There are web browsers for monochromatic displays or even for blind people, so of course, there are ranges of implementations.