Creating a triangle in css with a gradient background

Question

I am trying to create a triangle in css with a gradient background. I have not had any success as yet. Is there way to do this to bring off this effect seen in the image below. (The triangle that is attached to the Wrong password error box.)

Design in Photoshop

This is the design I have so far in HTML and CSS.

Here is the css I have for the triangle at the moment.

.error-triangle {
    wwidth: 0;
    height: 0;
    border-top:    10px solid transparent;
    border-bottom: 10px solid transparent;
    border-right:  10px solid blue;
    margin-top: 64px;
    margin-left: 350px;
    position: fixed;
    -webkit-box-shadow: 0 0 3px rgba(102,65,65,.25), 2px 3px 5px rgba(70,34,34,.25), inset 1px 2px rgba(255,255,255,.25);
       -moz-box-shadow: 0 0 3px rgba(102,65,65,.25), 2px 3px 5px rgba(70,34,34,.25), inset 1px 2px rgba(255,255,255,.25);
            box-shadow: 0 0 3px rgba(102,65,65,.25), 2px 3px 5px rgba(70,34,34,.25), inset 1px 2px rgba(255,255,255,.25);
    background-image: -webkit-linear-gradient(bottom, #eb6767, #d94040 35%, #eb6767);
    background-image:    -moz-linear-gradient(bottom, #eb6767, #d94040 35%, #eb6767);
    background-image:      -o-linear-gradient(bottom, #eb6767, #d94040 35%, #eb6767);
    background-image:     -ms-linear-gradient(bottom, #eb6767, #d94040 35%, #eb6767);
    background-image:         linear-gradient(to top, #eb6767, #d94040 35%, #eb6767);
}

I was using this tutorial on CSS tricks.

Answer 1

Creating triangles (or other shapes - pentagons, hexagons, octagons, decagons, dodecagons, tetradecagons, octadecagons and so on) with a gradient (or any other kind of image background) is really easy with CSS transforms.

But in this case you don't even need a triangle. You just need to rotate a square pseudo-element by 45deg and apply the gradient on that from corner to corner.

demo

<div class='warn'></div>

CSS:

.warn {
  position: relative;
  margin: 0 auto;
  border: solid 1px darkred;
  width: 12em; height: 3em;
  border-radius: .2em;
  background: linear-gradient(lightcoral, firebrick);
}
.warn:before {
  position: absolute;
  top: 50%; left: 0;
  margin: -.35em -.45em;
  border-left: inherit; border-bottom: inherit;
  /* pick width & height such that 
     the diagonal of the square is 1em = 1/3 the height of the warn bubble */
  width: .7em; height: .7em;
  border-radius: 0 0 0 .2em;
  transform: rotate(45deg);
  background: linear-gradient(-45deg, firebrick -100%, lightcoral 200%);
  content: '';
}