瀏覽器的User Agent Styles

Every browser has a predefined set of styles used as an initial base point when rendering a web page. These styles are commonly referred to as User Agent Styles. In the Chrome Dev tools, these styles are denoted by a gray background.

https://stackoverflow.com/questions/40271537/why-are-css-styles-greyed-out-in-chrome-developer-tools

每個瀏覽器都有一套預定義的樣式規則，作爲渲染web頁面的默認樣式規則使用。這些默認樣式被稱作User Agent Styles. 在Chrome開發者工具裏，這些styles被標註成灰色背景。