Colloid-gtk-theme/src/sass/gnome-shell/widgets-47-0/_notifications.scss

/* Notifications & Message Tray */

$notification_banner_height: 64px;
$notification_banner_width: 34em;

// Banner notifications
.notification-banner {
  min-height: $notification_banner_height;
  width: $notification_banner_width;
  margin: 12px 8px 8px;
  border-radius: $base_radius;
  color: $text-secondary;
  background-color: $popover;
  text-shadow: none;
  border-radius: $menu_radius;

  @if $rimless == 'false' and $variant == 'dark' {
    border: 1px solid $window-border;
    box-shadow: inset 0 0 0 1px highlight($popover);
  } @else {
    border: none;
    box-shadow: 0 3px 6px rgba(black, 0.25);
  }

  &:hover, &:active, &:focus {
    color: $text;
    background-color: $popover;
  }
}

.notification-buttons-bin {
  background-color: transparent;
  padding-top: 0;
  border: none;
  border-top: 1px solid $border;
  spacing: 0;
}

.notification-button {
  min-height: $item_size + $base_padding * 2;
  padding: 0 $base_padding * 3;
  background-color: transparent;
  color: $text-secondary;
  font-weight: 500;
  border: none;

  &:focus {
    background-color: transparent;
    color: $text;
    box-shadow: inset 0 0 0 2px $divider;
  }

  &:hover, &:focus:hover {
    background-color: $divider;
    color: $text;
    box-shadow: none;
  }

  &:active {
    background-color: $track;
    color: $text;
  }

  &:first-child:ltr {
    border-radius: 0 0 0 $menu_radius;
  }

  &:last-child:ltr {
    border-radius: 0 0 $menu_radius;
    margin-right: 0 !important;
  }

  &:first-child:rtl {
    border-radius: 0 0 $menu_radius;
  }

  &:last-child:rtl {
    border-radius: 0 0 0 $menu_radius;
    margin-left: 0 !important;
  }

  &:first-child:last-child {
    border-radius: 0 0 $menu_radius $menu_radius;
    margin-left: 0 !important;
    margin-right: 0 !important;
  }
}