<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;
}