hamburger in squarpace 7.1

Hi, can anyone please provide small  help in a custom code for hamburger. the code i have produces 2 lines in hamburger icon while hamburger usually have three lines not two so what should i do to make it three. here is the code attached.

.header-burger { display:flex!important}
.header--menu-open .header-menu {opacity: 1!important;visibility: visible!important;}
.header-nav, .header-actions {visibility:hidden!important}

Add to Home > Design > Custom CSS

.burger-box div {
    display: none;
}
.burger-box {
    background-image: url(https://image.flaticon.com/icons/svg/876/876207.svg);
    background-size: contain;
    background-repeat: no-repeat;
    background-position: center center;
}