<div class="box">
  <p>「top」以外透明</p>
  <div class="example top"></div>
</div>

<div class="box">
  <p>「left」以外透明</p>
  <div class="example left"></div>
</div>

<div class="box">
  <p>「right」以外透明</p>
  <div class="example right"></div>
</div>

<div class="box">
  <p>「bottom」以外透明</p>
  <div class="example bottom"></div>
</div>

* {
  box-sizing: border-box;
}
body {
  min-height: 100vh;
  margin: 0;
  padding: 0;
  display: flex;
  justify-content: center;
  align-items: center;
}
.box {
  text-align: center;
}
.box:not(:last-of-type) {
  margin-right: 5%;
}
.example {
  border-top: 20px solid #a0dde2;
  border-left: 20px solid #e2a0b4;
  border-right: 20px solid #eec496;
  border-bottom: 20px solid #a0e2c2;
  display: inline-block;
}
.example.top {
  border-color: #a0dde2 transparent transparent transparent;
}
.example.left {
  border-color: transparent transparent transparent #e2a0b4;
}
.example.right {
  border-color: transparent #eec496 transparent transparent;
}
.example.bottom {
  border-color: transparent transparent #a0e2c2 transparent;
}