Vite hmr fix (#781)

Author: Ben Jervis

.changeset/five-students-try.md

@@ -0,0 +1,5 @@
+---
+'@vanilla-extract/vite-plugin': patch
+---
+
+Adds a check for the existence of import.meta.hot before attempting to add an event listener to inject styles

packages/vite-plugin/src/index.ts

@@ -114,9 +114,11 @@ export function vanillaExtractPlugin({
 
         inject(${JSON.stringify(css)});
 
-        import.meta.hot.on('${styleUpdateEvent(validId)}', (css) => {
-          inject(css);
-        });
+        if (import.meta.hot) {
+          import.meta.hot.on('${styleUpdateEvent(validId)}', (css) => {
+            inject(css);
+          });
+        }
       `;
     },
     async transform(code, id, ssrParam) {