perf[ThemePicker]: refine updateStyle function (#554)

* theme replacing should cut tons of irrelevant css

Author: WangXinhai

src/components/ThemePicker/index.vue

@@ -67,11 +67,18 @@ export default {
 
   methods: {
     updateStyle(style, oldCluster, newCluster) {
-      let newStyle = style
+      const colorOverrides = [] // only capture color overides
       oldCluster.forEach((color, index) => {
-        newStyle = newStyle.replace(new RegExp(color, 'ig'), newCluster[index])
+        const value = newCluster[index]
+        const color_plain = color.replace(/([()])/g, '\\$1')
+        const repl = new RegExp(`(^|})([^{]+{[^{}]+)${color_plain}\\b([^}]*)(?=})`, 'gi')
+        const nestRepl = new RegExp(color_plain, 'ig') // for greed matching before the 'color'
+        let v
+        while ((v = repl.exec(style))) {
+          colorOverrides.push(v[2].replace(nestRepl, value) + value + v[3] + '}') // '}' not captured in the regexp repl to reserve it as locator-boundary
+        }
       })
-      return newStyle
+      return colorOverrides.join('')
     },
 
     getCSSString(url, callback, variable) {