By default on the mobile version you have to click on the + icon to expand the menu but using the CSS code below, I am able to show one level submenu item by default. The theme for the website is The7 . The CSS code should be implemented in Theme Options -> Advanced -> Custom CSS
#mobile-menu>.menu-item>.sub-nav{
display: block !important;
}
#mobile-menu>.menu-item>.next-level-button{
display:none;
}
Then Symagic asked for showing all the submenu items by default on the mobile version instead of one level. The CSS code below is the one and should be replaced with the previous one and should be implemented in Theme Options -> Advanced -> Custom CSS
#mobile-menu .menu-item .sub-nav{
display: block !important;
}
#mobile-menu .menu-item .next-level-button{
display:none;
}