If you're struggling with implementing box shadow in older versions of Internet Explorer, it's important to remember that these browsers are outdated and may not be worth the effort. Instead of trying to make IE 5 or similar browsers work like modern ones, consider utilizing progressive enhancement or graceful degradation techniques. This way, newer browsers can take advantage of advanced features while older ones still function without breaking entirely. Check out this informative article from the W3C for more insights.
Ultimately, focusing on compatibility with such ancient browsers could be an instance of the XY problem. Rather than obsessing over making IE 5 look modern, ask yourself if it's necessary to support these browsers at all. Statistics show that IE 5 accounts for only a tiny fraction of web traffic nowadays, so the answer is likely no. Save yourself the hassle and prioritize optimizing for more widely used browsers. Take a look at Net Market Share's stats to see just how insignificant IE 5 has become in today's digital landscape.