triangle

.menu_triangle {
    position: absolute;
    top: 0;
    left: 0;
    width: 6px;
    height: 10px;
    transform: translateX(-5px);
    transition: transform 0.5s;
}
.menu_triangle::after, .menu_triangle::before {
    top: 0;
    left: 0;
    border: solid transparent;
    content: " ";
    height: 0;
    width: 0;
    position: absolute;
    pointer-events: none;
    transition: transform 0.3s;
}
.menu_triangle::before {
    border-color: rgba(229, 37, 33, 0);
    border-top-color: #e52521;
    border-width: 5px;
    margin-left: -5px;
}