element-web/res/themes/light/css/_mods.scss

// sidebar blurred avatar background
//
// if backdrop-filter is supported,
// set the user avatar (if any) as a background so
// it can be blurred by the tag panel and room list

.mx_RoomSublist_showNButton {
    background-color: transparent !important;
}

a:hover,
a:link,
a:visited {
    text-decoration: none;
}