.main_menu_panel {
    z-index: 1000;
    position: fixed;
    top: 80px;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.8);
    overflow: auto;

    max-height: 0;
    overflow: hidden;
    opacity: 0;
    transition: max-height 0.5s ease, opacity 0.5s ease;
}
.main_menu_panel.show {
    max-height: 100%;
    opacity: 1;
}
.main_menu_item.active {
    background-color: #FFFFFF !important;
    border: 1px solid #CCCCCC !important;
    border-radius: 3px !important;
}
.sub_menu_panel {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    max-height: 0;
    overflow: hidden;
    opacity: 0;
    transition: max-height 0.5s ease, opacity 0.5s ease;
}
.sub_menu_panel.show {
    max-height: 100%;
    opacity: 1; 
}