gnome-shell/data/theme/gnome-shell-sass/widgets/_screen-shield.scss

/* Screen Shield */

$_unlockdialog_shadow: 0px 0px 6px rgba(0, 0, 0, 0.726);

.unlock-dialog-clock {
  color: white;
  text-shadow: $_unlockdialog_shadow;
  font-weight: bold;
  text-align: center;
  padding-bottom: 1.5em;
}

.unlock-dialog-clock-time {
  font-size: 72pt;
  text-shadow: $_unlockdialog_shadow;
  font-feature-settings: "tnum";
}

.unlock-dialog-clock-date {
  font-size: 28pt;
  font-weight: normal;
}

.unlock-dialog-notifications-container {
  spacing: 6px;
  width: 30em;
  background-color: transparent;
  max-height: 500px;
  .summary-notification-stack-scrollview {
    padding-top: 0;
    padding-bottom: 0;
  }

  .notification,
  .unlock-dialog-notification-source {
    padding: 12px 6px;
    border: 1px solid $osd_outer_borders_color;
    background-color: transparentize($osd_bg_color,0.5);
    color: $osd_fg_color;
    border-radius: 4px;
  }
  .notification { margin-right: 15px; } //compensate for space allocated to the scrollbar
}


.unlock-dialog-notification-label {
  font-weight: bold;
  padding: 0px 0px 0px 12px;
}

.unlock-dialog-notification-count-text { padding: 0px 0px 0px 12px; }

#panel.lock-screen { background-color: transparentize($osd_bg_color, 0.5); }

.screen-shield-background { //just the shadow, really
  background: black;
  box-shadow: 0px 2px 4px rgba(0,0,0,0.6);
}

#lockDialogGroup {
  background: lighten(#2e3436, 8%) url(resource:///org/gnome/shell/theme/noise-texture.png);
  background-repeat: repeat;
}

#unlockDialogNotifications {
  StButton#vhandle, StButton#hhandle {
    background-color: transparentize($bg_color,0.7);
    &:hover, &:focus { background-color: transparentize($bg_color,0.5); }
    &:active { background-color: transparentize($selected_bg_color,0.5); }
  }
}