How to take off the border on the flagbox?

You can copy this CSS rule in your custom CSS file or in the advanced settings of Linguise plugin within the Custom CSS fields:

				
					/* remove background color */
.linguise_switcher{
    background-color: transparent !important;
}

/* remove border */
#dropdown .linguise_switcher_dropdown li{
    border-bottom: none !important;
}

#dropdown .linguise_switcher_dropdown li.linguise_current .linguise_current_lang{
    border: none !important;
}