How to triangle top and bottom border?

Question

As you can see in the image below, I am trying to warp or triangle my div from bottom and top, but I have no idea how to do it. I just tried a couple of times to do it, but

Answer 1

An idea using transformation and perspective where you will have the border, border-radius also the gradient:

body {
  background: lightblue;
}

.block {
  overflow: hidden;
  width: 300px;
  height: 200px;
  margin: 20px;
  position: relative;
  z-index:0;
}

.block::before,
.block::after {
  content: "";
  position: absolute;
  z-index:-1;
  border: 1px solid #fff;
  top: 0;
  bottom: 0;
  width: 50%;
  background-image: linear-gradient(to right, #314b56, #283b44, #1f2c32, #161e21, #0a0f11);
  background-size: 200% 100%;
}

.block::before {
  left: 0;
  border-right: 0;
  border-radius: 15px 0 0 15px;
  transform-origin: right;
  transform: perspective(100px) rotateY(-5deg);
}

.block::after {
  right: 0;
  border-left: 0;
  border-radius: 0 15px 15px 0;
  transform-origin: left;
  transform: perspective(100px) rotateY(5deg);
  background-position: right;
}

You can also add the shadow and easily change the gradient:

body {
  background: lightblue;
}

.block {
  overflow: hidden;
  width: 300px;
  height: 200px;
  margin: 20px;
  position: relative;
  z-index:0;
  filter:drop-shadow(0 0 5px #000);
}

.block::before,
.block::after {
  content: "";
  position: absolute;
  z-index:-1;
  border: 1px solid #fff;
  top: 0;
  bottom: 0;
  width: 50%;
  background-image: linear-gradient(35deg, blue, red);
  background-size: 200% 100%;
}

.block::before {
  left: 0;
  border-right: 0;
  border-radius: 15px 0 0 15px;
  transform-origin: right;
  transform: perspective(100px) rotateY(-5deg);
}

.block::after {
  right: 0;
  border-left: 0;
  border-radius: 0 15px 15px 0;
  transform-origin: left;
  transform: perspective(100px) rotateY(5deg);
  background-position: right;
}