SOURCE

<div class="triangle">
  <div class="left"><div></div></div>
  <div class="right"><div></div></div>
  <div class="bottom"><div></div></div>
</div>

html {
  height: 100%;
}

body {
  margin: 0;
  background: radial-gradient(ellipse at center, 
              rgba(44,62,80,1) 0%, 
              rgba(52,152,219,1) 92%, 
              rgba(52,152,219,1) 100%);
  overflow: hidden;
  margin: auto;
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  width: 500px;
  height: 500px;
}

.triangle {
  margin: 0 auto;
  transform: scale(0.4,0.4);
  height: 500px;
}

.left {
  width: 140px;
  height: 500px;
  transform: rotate(30deg);
  position: absolute;
  left: 0;
  top: 0;
  z-index: 1;
}

.left div {
  transform: rotate(30deg) skew(30deg);
  background: #006495;
  width: 100%;
  height: 500px;
}

.left div:after {
  content: "";
  background: #006495;
  width: 330px;
  height: 100px;
  position: absolute;
  right: -325px;
}

.right {
  width: 140px;
  height: 500px;
  transform: rotate(-30deg);
  position: absolute;
  left: 323px;
  top: -60px;
  z-index: 99;
}

.right div {
  transform: rotate(30deg) skew(30deg);
  background: #0093D1;
  width: 100%;
  height: 500px;
  position: absolute;
  right: 0;
}

.right div:after {
  content: "";
  background: #0093D1;
  width: 322px;
  height: 100px;
  position: absolute;
  right: 82px;
  bottom: 0;
  transform: skew(-49deg);
}

.bottom {
  width: 140px;
  height: 500px;
  transform: rotate(90deg);
  position: absolute;
  left: 214px;
  top: 250px;
}

.bottom div {
  transform: rotate(30deg) skew(30deg);
  background: #004C70;
  width: 100%;
  height: 500px;
  position: absolute;
  right: 0;
}

.bottom div:after {
  content: "";
  background: #004C70;
  width: 462px;
  height: 100px;
  position: absolute;
  right: 0;
  top: 400px;
}