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

/* Modal Dialogs */

.headline {
  @include fontsize($base_font_size + 1);
}

.modal-dialog {
  border-radius: $modal_radius;
  @extend %bubble_panel;

  .modal-dialog-content-box {
    margin: 32px 40px;
    spacing: 32px;
    max-width: 28em;
  }

  .modal-dialog-linked-button {
    @extend %bubble_button;
  }
}

/* End Session Dialog */
.end-session-dialog {
  width: 30em;

  .end-session-dialog-battery-warning,
  .dialog-list-title {
    color: $warning_color;
  }
}

/* Message Dialog */
.message-dialog-content {
  spacing: 18px;

  .message-dialog-title {
    text-align: center;
    font-size: 18pt;
    font-weight: 800;

    &.lightweight {
      font-size: 13pt;
      font-weight: 800;
    }
  }
  .message-dialog-description { text-align: center; }
}

/* Dialog List */
.dialog-list {
  spacing: 18px;

  .dialog-list-title {
    text-align: center;
    font-weight: bold;
  }

  .dialog-list-scrollview { max-height: 200px; }
  .dialog-list-box {
    spacing: 1em;

    .dialog-list-item {
      spacing: 1em;

      .dialog-list-item-title { font-weight: bold; }
      .dialog-list-item-description {
        color: darken($fg_color,5%);
        @include fontsize($base_font_size - 1);
      }
    }
  }
}

/* Run Dialog */
.run-dialog {
  .modal-dialog-content-box {
    margin-top: 24px;
    margin-bottom: 14px;
  }
  .run-dialog-entry { width: 20em; }
  .run-dialog-description {
    @include fontsize($base_font_size - 1);
    text-align: center;
    color: darken($fg_color, 20%);
  }
}

/* Password or Authentication Dialog */

.prompt-dialog {
  width: 28em;

  .modal-dialog-content-box {
    margin-bottom: 24px;
  }
}

.prompt-dialog-password-grid {
  spacing-rows: 8px;
  spacing-columns: 4px;

  .prompt-dialog-password-entry {
    width: auto;

    // 4px (spacing) + 16px (spinner-width)
    &:ltr { margin-left: 20px; }
    &:rtl { margin-right: 20px; }
  }
}

.prompt-dialog-password-layout {
  spacing: 8px;
}

.prompt-dialog-password-entry {
  width: 20em;
}

.prompt-dialog-error-label,
.prompt-dialog-info-label,
.prompt-dialog-null-label {
  text-align: center;
  @include fontsize($base_font_size - 1);
}

.prompt-dialog-error-label {
  color: $warning_color;
}


/* Polkit Dialog */

.polkit-dialog-user-layout {
  text-align: center;
  spacing: 8px;
  margin-bottom: 6px;

  .polkit-dialog-user-root-label { color: $warning_color; }
}

/* Audio selection dialog */
.audio-device-selection-dialog {
  .modal-dialog-content-box { margin-bottom: 28px; }
  .audio-selection-box { spacing: 20px; }
}

.audio-selection-device {
  border: 1px solid $bubble_borders_color;
  border-radius: 12px;
  &:hover,&:focus { background-color: $hover_bg_color; }
  &:active { 
    background-color: $selected_bg_color;
    color: $selected_fg_color;
  }
}

.audio-selection-device-box {
  padding: 20px;
  spacing: 20px;
}

.audio-selection-device-icon {
  icon-size: $base_icon_size * 4;
}

/* Welcome dialog */
.welcome-dialog-image {
  background-image: url("resource:///org/gnome/shell/theme/gnome-shell-start.svg");
  background-size: contain;
  /* Reasonable maximum dimensions */
  height: 300px;
  width: 300px;
}