WhiteSur-gtk-theme/src/sass/gnome-shell/common/_panel.scss

/* Top Bar */
// a.k.a. the panel

@if $trans == 'true' { $panel_bg:   if($variant == 'light', rgba(white, $panel_opacity), rgba(black, $panel_opacity)); }
$shell_panel_bg: if($trans == 'true', $panel_bg, rgba($panel_bg, 0.95));

#panel {
  background-color: $shell_panel_bg;
  transition-duration: 250ms;
  font-weight: bold;
  height: $menuitem_size;
  box-shadow: 0 5px 16px rgba(black, 0.35);
  color: $panel_fg;
  font-feature-settings: "tnum";
  transition-duration: 250ms;

  // transparent panel on lock & login screens
  &:overview,
  &.unlock-screen,
  &.login-screen,
  &.lock-screen {
    background-color: if($trans == 'false' and $variant == 'light', transparent, transparent);

    StLabel, StIcon { color: $light_alt_fg_color; }

    .panel-button {
      &:hover {
        color: $light_fg_color;
        background-color: $light_divider_color;
      }

      &:active, &:overview, &:focus, &:checked {
        &, &:hover {
          color: $light_fg_color;
          background-color: $light_track_color;
        }
      }
    }

    .panel-corner {
      -panel-corner-radius: 0;
      -panel-corner-background-color: transparent;
      -panel-corner-border-color: transparent;
    }
  }

  // the rounded outset corners
  .panel-corner {
    -panel-corner-radius: 0;
    -panel-corner-background-color: $shell_panel_bg;
    -panel-corner-border-width: 2px;
    -panel-corner-border-color: transparent;
    -panel-corner-opacity: 1;
    transition-duration: 250ms;
  }

  // panel menus
  .panel-button {
    -natural-hpadding: 8px;
    -minimum-hpadding: 8px;
    font-weight: bold;
    color: $panel_fg;
    transition-duration: 150ms;
    border-radius: $bt_radius;

    StLabel { padding: 0 2px; }

    &, &:hover, &:active, &:overview, &:focus, &:checked {
      text-shadow: $panel_asset_shadow;

      .system-status-icon,
      .app-menu-icon > StIcon,
      .popup-menu-arrow {
        icon-shadow: $panel_asset_shadow;
      }
    }

    &:hover {
      color: $panel_fg;
      background-color: if($trans == 'false' and $variant == 'light', $divider_color, $light_divider_color);
    }

    &:active, &:overview, &:focus, &:checked {
      &, &:hover {
        background-color: if($trans == 'false' and $variant == 'light', $track_color, $light_track_color);
        color: $panel_fg;
        box-shadow: none;
      }
    }

    .unlock-screen &,
    .login-screen &,
    .lock-screen & {
      color: $panel_fg;
      &:focus, &:hover, &:active { color: $panel_fg; }
    }

    &.clock-display {
      .clock {
        // transition-duration: 150ms;
        border: none;
        border-radius: 0;
        background: none;
        box-shadow: none;
      }
    }

    &:hover, &:active, &:overview, &:focus, &:checked {
      box-shadow: none;

      // The clock display needs to have the background on .clock because
      // we want to exclude the do-not-disturb indicator from the background
      &.clock-display {
        box-shadow: none;

        .clock {
          box-shadow: none;
        }
      }
    }

    // status area icons
    .system-status-icon {
      icon-size: $base_icon_size;
      padding: $base_padding - 1px;
      margin: 0 $base_margin;
    }

    .panel-status-indicators-box .system-status-icon,
    .panel-status-menu-box .system-status-icon {
      margin: 0;
    }

    // app menu icon
    .app-menu-icon {
      -st-icon-style: symbolic;
      // dimensions of the icon are hardcoded
    }

    &#panelActivities {
      -natural-hpadding: $base_padding * 3;
    }
  }

  &.unlock-screen,
  &.login-screen,
  &:overview {
    .panel-button {
      &:hover, &:active, &:overview, &:focus, &:checked {
        box-shadow: none;

        &.clock-display {
          box-shadow: none;

          .clock {
            box-shadow: none;
          }
        }
      }
    }
  }

  .panel-status-indicators-box,
  .panel-status-menu-box {
    spacing: 2px;
  }

  // spacing between power icon and (optional) percentage label
  .power-status.panel-status-indicators-box {
    spacing: 0;
  }

  // indicator for active
  .screencast-indicator,
  .remote-access-indicator { color: $warning_color; }
}

// Activities button
#panel #panelActivities.panel-button {
  > * {
    background-image: url("assets/activities.svg");
    background-position: center top;
    // background-size: 18px 18px;
    width: 24px;
    height: 24px;
    background-color: transparent !important;
    background-gradient-direction: none !important;
    border: none;
    color: transparent;
  }

  &:active, &:overview, &:focus, &:checked {
    background-color: transparent;
    border: none;

    // > * { background-image: url("assets/activities-active.svg"); }
  }

  @if $variant == 'light' and $black == 'true' {
    &:overview {
      > * { background-image: url("assets/activities-white.svg"); }
    }
  }
}