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.top-menu .sub-menu ul[data-depth="1"]>li {
    margin: 0 1.25rem;
    clear: both;
}
.popover {
    position: absolute;
    top: 0;
    /* left: 0; */
    z-index: 1060;
    display: block;
    max-width: 200px;
    padding: 1px;
    font-family: -apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,sans-serif;
    font-style: normal;
    font-weight: 400;
    letter-spacing: normal;
    line-break: auto;
    line-height: 1.5;
    text-align: left;
    text-align: start;
    text-decoration: none;
    text-shadow: none;
    text-transform: none;
    white-space: normal;
    word-break: normal;
    word-spacing: normal;
    font-size: .875rem;
    word-wrap: break-word;
    background-color: #fff;
    background-clip: padding-box;
    border: 1px solid rgba(0,0,0,.2);
    border-radius: .3rem;
}
.sub-menu {
    left: auto;
    min-width: 50%;
}

.top-menu .sub-menu {
    box-shadow: 2px 1px 11px 2px rgba(0,0,0,.1);
    border: none;
    margin-left: .9375rem;
    width: inherit;
    min-width: inherit;
    z-index: 18;
    display: none;
}

Adding these lines to customm.css is the correct solution to the problem: