fix(block-snapshot): change the canvas selector to #app (#1514)

Author: betterdancing

packages/plugins/block/src/js/blockSetting.tsx

@@ -384,7 +384,7 @@ export const initEditBlock = (block) => {
 export const getBlockBase64 = () => {
   const iframe = document.querySelector('#canvas')
   const subDocument = iframe.contentWindow.document
-  const container = subDocument.querySelector('.design-page')
+  const container = subDocument.querySelector('#app')
 
   return html2canvas(container, { useCORS: true })
     .then((canvas) => canvas.toDataURL('image/webp'))