gnome-shell/data/theme/gnome-shell-sass/widgets/_notifications.scss

/* Notifications & Mesage Tray */

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

// Banner notifications
.notification-banner {
  min-height: $notification_banner_height;
  width: $notification_banner_width;
  font-size: $base_font_size;
  margin: $base_margin;
  border-radius: $modal_radius;

  .message-title { color: $fg_color }
  .message-content { color: $fg_color; }

  &:hover { background: $bg_color; }
  &, &:focus, &:active {
    background-color: $bg_color;
    .message-title { color: $fg_color }
    .message-content { color: $fg_color; }
  }

  // icon
  .message-icon-bin > StIcon {
    icon-size: $base_icon_size * 2;
    color: $fg_color;
  }

  // entries
  StEntry { @extend %bubble_entry; }

  .notification-icon {
    padding: 5px;
  }

  .notification-content {
    padding: 5px;
    spacing: 5px;
  }

  .secondary-icon { icon-size: $base_icon_size; }

  .notification-actions {
    padding-top: 0;
    color: $fg_color;
    border-top: 1px solid $bubble_borders_color;
    spacing: 0;
  }

  .notification-button {
    @extend %bubble_button;
    min-height: $notification_banner_height * 0.5;
    padding: $base_padding !important;
    border-top-width: 0 !important;
    
    &:focus { box-shadow: none; }
  }
}

// counter
.summary-source-counter {
  font-size: $base_font_size - 1pt;
  font-weight: bold;
  height: 1.6em;
  width: 1.6em;
  -shell-counter-overlap-x: 3px;
  -shell-counter-overlap-y: 3px;
  background-color: $selected_bg_color;
  color: $selected_fg_color;
  border: 2px solid $fg_color;
  box-shadow: 0 2px 2px rgba(0,0,0,0.5);
  border-radius: 0.9em; // should be 0.8 but whatever; wish I could do 50%;
}

.secondary-icon { icon-size: $base_icon_size; }

// chat bubbles
.chat-body { spacing: 5px; }
.chat-response { margin: 5px; }
.chat-log-message { color: darken($fg_color,10%); }
.chat-new-group { padding-top: 1em; }
.chat-received {
  padding-left: 4px;
  &:rtl { padding-left: 0px; padding-right: 4px; }
}

.chat-sent {
  padding-left: 18pt;
  color: lighten($fg_color, 15%);
  &:rtl { padding-left: 0; padding-right: 18pt; }
}

.chat-meta-message {
  padding-left: 4px;
  font-size: 9pt;
  font-weight: bold;
  color: lighten($fg_color,18%);
  &:rtl { padding-left: 0; padding-right: 4px; }
}