There is no universal language used by every single person in the world, and there’s also no universal browser. This doesn’t tend to be an issue in everyday life. However, this can become a huge issue for you if you decide to buy a WordPress theme that isn’t compatible with all major browsers, but instead only looks good in one or two of them. While one person might be a diehard Chrome user, another might be absolutely in love with Firefox. So, is it fair that only one of these people will be able to easily view your website? Absolutely not. Not only will it become an upsetting situation for the wannabe site viewer, but it will most definitely become an upsetting situation for you as well. If your WordPress theme isn’t built for viewing in all major web browsers, you are not going to be happy with your numbers at the end of the day, month, and year. In fact, you’re basically setting yourself up for failure as soon as you select such a theme.
If your WordPress theme creates an absolutely fantastic experience for site viewers using one browser, but a crummy experience for site viewers using another, it’s time to move on and choose a different one. With so many cross-browser compatible themes in existence, it’s absolute insanity to choose one that’s not. Why would you ever want to limit yourself and your potential fanbase? If everybody can view your website, then everybody can love it. And the love of the people is what you ultimately need for high numbers and a huge success.