remove header boarder

Hello Enfold Team,

I am trying to remove the border from my transparent header, but a thin black line persists whenever I start to scroll down the page. I have applied all of the following CSS, but unfortunately, not have done the trick for me.

#header_main {
border-bottom: none!important;
}

.av-main-nav > li > a {
border: none!important;
}

#top .av_header_with_border.avia-menu.av_menu_icon_beside, #top .av_header_with_border #header_main, .av-main-nav > li > a {
border: none!important;
}

#header .main_menu .avia-menu-fx {
display: none !important;
}

Thanks in advance for your help.

-James