Top browser compatibility issues in CSS for developers in 2021 are being addressed by Google, Microsoft, and other tech giants. The top five focus areas include CSS Flexbox, CSS Grids, CSS position: sticky, CSS aspect-ratio, and CSS transforms. These properties are extremely popular and used extensively in web application development. Google has collaborated with Microsoft and Igalia to divide this work and proceed faster. Browser compatibility testing tools like LambdaTest support 3000+ browsers and browser combinations across different platforms and operating systems on the cloud. Developers can perform cross-browser testing on locally hosted web applications for unpublished websites or under-development websites. To solve browser compatibility issues in CSS, developers should prioritize rendering their website on major browsers, use cross-browser testing platforms, and raise bugs to let experts handle them.