feat: customize the theme color

src/polyfill.js

@@ -0,0 +1,27 @@
+import { load } from './util'
+
+function replaceVar (block) {
+  block.innerHTML = block.innerHTML.replace(/var\(\s*--theme-color.*?\)/g, __docsify__.themeColor)
+}
+
+export function cssVars () {
+  // variable support
+  if (window.CSS && window.CSS.supports && window.CSS.supports('(--foo: red)')) return
+
+  const styleBlocks = document.querySelectorAll('style:not(.inserted),link')
+
+  ;[].forEach.call(styleBlocks, block => {
+    if (block.nodeName === 'STYLE') {
+      replaceVar(block)
+    } else if (block.nodeName === 'LINK') {
+      load(block.getAttribute('href'))
+        .then(res => {
+          const style = document.createElement('style')
+
+          style.innerHTML = res
+          document.head.appendChild(style)
+          replaceVar(style)
+        })
+    }
+  })
+}