fix style css in ts

src/utils/image.ts

@@ -28,7 +28,13 @@ function fileToBase64(file: File): Promise<string> {
 	return new Promise((resolve, reject) => {
 		const reader = new FileReader()
 		reader.readAsDataURL(file)
-		reader.onload = () => resolve(reader.result as string)
+		reader.onload = () => {
+		  if (typeof reader.result === 'string') {
+		    resolve(reader.result)
+		  } else {
+		    reject(new Error('Unexpected file reader result type'))
+		  }
+		}
 		reader.onerror = () => reject(new Error('Failed to read file'))
 	})
 }