Question: Trying to create a transparent triangle div with a colored border.

css

```
#down {
 display: block;
 position: fixed;
 left: 0; right: 0;
 width: 0; height: 0;
 margin: 0 auto;
 border-left: 55px solid transparent;
 border-right: 55px solid transparent;
 z-index: 20; 
 bottom: 0; 
 border-bottom: 55px solid rgba(250,250,250,0.75); 
}

```

putting a div on-top another div ruins the transparency

Answer: 
You can also use gradients and/or transform:

* on left: square + border-top/left + transform + gradient to draw the bottom border:
* on middle : yours
* on right : border-bottom + gradient for the triangle top borders

[both extra example can hold content](http://codepen.io/gc-nomade/pen/pyQjyq) such as font icone / text / image .

```css
body {
  background:tomato;
}

#rotate {
  position:fixed;
  border:solid turquoise;
  border-bottom:none;
  border-right:none;
  bottom:7px;
  left:calc(50% - 180px);
  height:75px;
  width:75px;
  transform-origin: bottom left;
  transform:rotate(45deg);
  background:linear-gradient(to bottom right, transparent calc(50% - 3px), turquoise calc(50% - 3px), turquoise 50%, transparent 50% ); 
}

#bg-gradient {
  position:fixed;
  bottom:5px;
  left: calc(50% + 70px)  ;
  border-bottom:solid turquoise;
  background:linear-gradient(to bottom right, transparent 50%, turquoise 50%, turquoise calc(50% + 3px), transparent calc(50% + 3px) ),linear-gradient(to bottom left, transparent 50%, turquoise 50%, turquoise calc(50% + 3px), transparent calc(50% + 3px) ) right
    ;
  background-repeat:no-repeat;
  background-size:50% 100%;
  height:55px;
  width:110px;

}

#down {
 display: block;
 position: fixed;
 left: 0; right: 0;
 width: 0; height: 0;
 margin: 0 auto;
 border-left: 55px solid transparent;
 border-right: 55px solid transparent;
 z-index: 20; 
 bottom: 5px; 
 border-bottom: 55px solid rgba(250,250,250,0.75); 
}
```

```html
<div id="down"></div>
<div id="rotate"></div>
<div id="bg-gradient"></div>
```

Notice that a rotated square at bottom can have half being hidden
This is usually done with border tricks, and those are not really helpful for this 

You need others techniques for that.

For instance, see this CSS

```
body {
    background: linear-gradient(90deg, lightblue, yellow)
}

.trapezoid {
    left: 50px;
    top: 50px;
    position: absolute;
    height: 100px;
    width: 500px;
    background-color: transparent;
}

.trapezoid:before {
    content: '';
    width: 57%;
    height: 100%;
    left: -4%;
    position: absolute;
    border-color: red;
    border-style: solid;
    border-width: 3px 0px 3px 3px;
    -webkit-transform: skewX(-20deg);
}

.trapezoid:after {
    content: '';
    width: 59%;
    height: 100%;
    right: -4%;
    position: absolute;
    border-color: red;
    border-style: solid;
    border-width: 3px 3px 3px 0px;
    -webkit-transform: skewX(20deg);
}

```