<div class="box">
	<p>左上</p>
	<div class="example ex01"></div>
</div>

<div class="box">
	<p>右上</p>
	<div class="example ex02"></div>
</div>

<div class="box">
	<p>右下</p>
	<div class="example ex03"></div>
</div>

<div class="box">
	<p>左下</p>
	<div class="example ex04"></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 {
	width: 0;
	height: 0;
}
.example.ex01 {
	border-style: solid;
	border-width: 30px 30px 0 0;
	border-color: #a0dde2 transparent transparent transparent;
}
.example.ex02 {
	border-style: solid;
	border-width: 0 30px 30px 0;
	border-color: transparent #e2a0b4 transparent transparent;
}
.example.ex03 {
	border-style: solid;
	border-width: 0 0 30px 30px;
	border-color: transparent transparent #eec496 transparent;
}
.example.ex04 {
	border-style: solid;
	border-width: 30px 0 0 30px;
	border-color: transparent transparent transparent #a0e2c2;
}