如何用CSS画三角形

    <div class="border-all-color"></div>
    <div class="border-left-color"></div>
    <div class="border-top-color"></div>
    <div class="border-right-color"></div>
    <div class="border-bottom-color"></div>

.border-all-color {
    margin: 20px auto;
    width: 0;
    height: 0;
    border-top: 40px solid coral;
    border-right: 40px solid lightblue;
    border-bottom: 40px solid lightgreen;
    border-left: 40px solid mediumpurple;
}

.border-left-color,
.border-top-color,
.border-right-color,
.border-bottom-color{
    width: 0;
    height: 0;
    margin: 10px auto;
    border: 20px solid transparent;
}

.border-left-color{
    border-left-color: #9370DB;
}
.border-top-color{
    border-top-color: #FF7F50;
}
.border-right-color{
    border-right-color: #ADD8E6;
}
.border-bottom-color{
     border-top-color: #90EE90;
 }