How is cross-browser support for CSS ensured?

Cross-browser CSS support is provided in several ways:

• Using vendor prefixes for properties that are not yet standardized or supported by all browsers (e.g., -webkit-, -moz-, -ms-).
• Checking property support with tools like Can I Use to understand which properties are supported in target browsers.
• Using CSS resets or normalizers (normalize.css) to eliminate default style differences.
• Applying progressive enhancement and graceful degradation — writing styles so that the site remains functional in older browsers, even if with a simplified design.
• Automating with preprocessors and postprocessors (e.g., PostCSS with autoprefixer plugin), which automatically add necessary prefixes.

Example of using autoprefixer in PostCSS:

/* Original CSS */
.example {
  display: flex;
}

After processing with autoprefixer, prefixes will be added:

.example {
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
}

This ensures compatibility across different browsers without manually adding prefixes.