Firefox DevTools now grays out CSS declarations that don’t have an effect on the page. When you hover over the info icon, you’ll see a useful message about why the CSS is not being applied, including a hint about how to fix the problem.
Firefox 开发者工具现在会将页面中无效的 CSS 声明显示为灰色。当您将鼠标悬停在信息图标上时，会看到该 CSS 规则未应用的原因，以及如何修正问题的提示。