CSS画出各种三角形如等边三角形

<div class="triangles"></div>

.triangles {
border: 50px solid transparent;
border-top-color: #0075a9;
border-right-color: #a89a00;
border-bottom-color: #19a800;
border-left-color: #a90000;
width: 0;
height: 0;
}

<div class="triangle v-top"></div>
<div class="triangle v-right"></div>
<div class="triangle v-bottom"></div>
<div class="triangle v-left"></div>

.triangle {
border: 30px solid transparent;
width: 0;
height: 0;
&.v-top {
border-top-color: #0075a9;
}
&.v-right {
border-right-color: #a89a00;
}
&.v-bottom {
border-bottom-color: #19a800;
}
&.v-left {
border-left-color: #a90000;
}
}

<div class="equilateral-triangle"></div>

.equilateral-triangle {
@side_length: 50px;
@altitude: (@side_length * ( sqrt(5) / 2 ) / 2);
border: @side_length solid transparent;
border-bottom-color: #19a800;
border-left-width: @altitude;
border-right-width: @altitude;
width: 0;
height: 0;
}