some html tweaking

index.html

@@ -12,7 +12,15 @@
 
       run();
     </script>
-	<canvas id="canvas" height="150" width="150"></canvas>
+    <style>
+        #circle_canvas{
+            position: absolute;
+            top: 50%;
+            left: 50%;
+            transform: translate(-50%, -50%);
+        }
+    </style>
+	<canvas id="circle_canvas" height="150" width="150"></canvas>
   </body>
 </html>
 

src/lib.rs

@@ -10,8 +10,9 @@ use circle::CircleShapes;
 
 #[wasm_bindgen(start)]
 pub fn start() {
+    let canvas_id = "circle_canvas";
     let document = web_sys::window().unwrap().document().unwrap();
-    let canvas = document.get_element_by_id("canvas").unwrap();
+    let canvas = document.get_element_by_id(canvas_id).unwrap();
     let canvas: web_sys::HtmlCanvasElement = canvas
         .dyn_into::<web_sys::HtmlCanvasElement>()
         .map_err(|_| ())