Question: I have this triangle in CSS:

```css
.triangle {
  width: 0;
  height: 0;
  border-style: solid;
  border-width: 200px 200px 0 0;
  border-color: #007bff transparent transparent transparent;
}
```

```html
<div class="triangle"></div>
```

How can I apply a 1px shadow on the hypotenuse line?

Answer: 
Since `box-shadow` won't work, you have to apply a drop shadow filter on the triangle:

```css
.triangle {
  width: 0;
  height: 0;
  border-style: solid;
  border-width: 200px 200px 0 0;
  border-color: #007bff transparent transparent transparent;
  -webkit-filter: drop-shadow(1px 1px 1px rgba(0,0,0,.5));
  filter: drop-shadow(1px 1px 1px rgba(0,0,0,.5));
}
```

```html
<div class="triangle"></div>
```
You can make this *without using borders* by employing an angled gradient.

```css
div {
  width: 200px;
  height: 200px;
  margin: 2em auto;
  background: linear-gradient(to bottom right, #007bff 50%, rgba(0,0,0,.5) 50%, transparent 52%);
}
```

```html
<div></div>
```