How to make triangle CSS

.triangle-up {
width: 0;
height: 0;
border-left: 25px solid transparent;
border-right: 25px solid transparent;
border-bottom: 50px solid #f5d040;
}

.triangle-down {
width: 0;
height: 0;
border-left: 25px solid transparent;
border-right: 25px solid transparent;
border-top: 50px solid #f5d040;
}

.triangle-left {
width: 0;
height: 0;
border-top: 25px solid transparent;
border-right: 50px solid #f5d040;
border-bottom: 25px solid transparent;
}

.triangle-right {
width: 0;
height: 0;
border-top: 25px solid transparent;
border-left: 50px solid #f5d040;
border-bottom: 25px solid transparent;
}