fix: missing resize-observer css

Author: Akryum

build/rollup.config.base.js

@@ -28,6 +28,8 @@ export default {
     }),
     css({
       output: styles => {
+        const file = require.resolve('vue-resize/dist/vue-resize.css')
+        styles += fs.readFileSync(file, { encoding: 'utf8' })
         fs.writeFileSync('dist/vue-virtual-scroller.css', new CleanCSS().minify(styles).styles)
       },
     }),