In general we support the 2 latest versions of major browsers like Chrome,Firefox,Edge,Safari and Opera. We support desktop,phone,tablet and the web view version of these respective browsers.@H_404_3@

Beyond that the core AMP library and builtin elements should aim for very wide browser support and we accept fixes for all browsers with market share greater than 1 percent.@H_404_3@

In particular,we try to maintain “it might not be perfect but isn’t broken”-support for the Android 4.0 system browser and Chrome 28+ on phones.@H_404_3@

从DEVELOPING.md#supported-browsers@H_404_3@

但是.. CSS变量？@H_404_3@

CSS自定义属性(也称为CSS变量)的使用是polyfilled：@H_404_3@

AMP HTML components that are more complex and nested … may be styled with an explicitly defined set of CSS Custom Properties. These are propagated to any children elements that are dynamically created by the runtime,to achieve the desired style.@H_404_3@

从spec/amp-html-components.md@H_404_3@