I am trying to give the border of a triangle that I made with css a box shadow.

```css
#triangle-topleft {
   width: 0;
   height: 0;
   border-top: 300px solid blue;
   border-right: 100px solid transparent;
  }
```

```html
<div id="triangle-topleft" />
```

I tried but can't give the right border a shadow. Is there an easy css way to accomplish this?
That's how it should look like in the end (just better with an actual shadow).

[![enter image description here](https://i.stack.imgur.com/uyUDf.png)](https://i.stack.imgur.com/uyUDf.png)