added css example

README.md

@@ -3,7 +3,7 @@ The library for creating creepy sticky background
 
 ## Example
 ```html
-<canvas class="wrap"></canvas>
+<canvas id="wrap"></canvas>
 
 <svg style="position: absolute">
   <defs>
@@ -39,6 +39,13 @@ import("/js/modules/womb3-simplex.mjs").then((module) => {
   }, true);
 });
 ```
+```css
+#wrap {
+  background-color: black; /* can be alpha 50% and etc */
+  filter: url("#blob") contrast(var(--contrast, 30));
+  /* mix-blend-mode: ... as you wish */
+}
+```
 
 ## Installation
 ```bash