Theme functions are used to render UI elements in a consistent way. There are theme functions defined for over 200 elements in Backdrop core, and while many of them are only used for special purposes, many others are used widely; all are available to developers.

Note that you should never call a theme function directly; instead of

$output = theme_something($variables);

you should call

$output = theme('something', $variables);

to allow for setting of default values, overrides, and modifications. See Default theme implementations for more details.

Function Location Summary
theme_admin_bar_links core/modules/admin_bar/admin_bar.theme.inc Render a themed list of links.
theme_admin_block core/modules/system/system.theme.inc Returns HTML for an administrative block for display.
theme_admin_block_content core/modules/system/system.theme.inc Returns HTML for the content of an administrative block.
theme_admin_page core/modules/system/system.theme.inc Returns HTML for an administrative page.
theme_authorize_message core/includes/theme.maintenance.inc Returns HTML for a single log message from the authorize.php batch operation.
theme_authorize_report core/includes/theme.maintenance.inc Returns HTML for a results report of an operation run by authorize.php.
theme_book_admin_table core/modules/book/book.admin.inc Returns HTML for a book administration form.
theme_breadcrumb core/includes/theme.inc Returns HTML for a breadcrumb trail.
theme_button core/includes/form.inc Returns HTML for a button form element.
theme_checkbox core/includes/form.inc Returns HTML for a checkbox form element.
theme_ckeditor5_settings_toolbar core/modules/ckeditor5/ckeditor5.theme.inc Displays the toolbar configuration for CKEditor.
theme_ckeditor_settings_toolbar core/modules/ckeditor/ckeditor.theme.inc Displays the toolbar configuration for CKEditor 4.
theme_color core/includes/form.inc Returns HTML for a color form element.
theme_color_preview core/modules/color/color.theme.inc Returns HTML for a theme's color preview.
theme_comment_block core/modules/comment/comment.theme.inc Returns HTML for a list of recent comments.
theme_comment_post_forbidden core/modules/comment/comment.theme.inc Returns HTML for a "you can't post comments" notice.
theme_common_test_foo core/modules/simpletest/tests/common_test.theme.inc Theme function for testing backdrop_render().
theme_confirm_form core/modules/system/system.theme.inc Returns HTML for a confirmation form.
theme_contact_category_list_table core/modules/contact/contact.theme.inc Returns HTML for the contact form categories administrative table.
theme_container core/includes/form.inc Returns HTML to wrap child elements in a container.
theme_date core/includes/form.inc Returns HTML for a date selection form element.
theme_datetime core/includes/theme.inc Returns HTML for a date / time.
theme_date_combo core/modules/date/date.theme.inc Returns HTML for a start/end date combination on form.
theme_date_display_combination core/modules/date/date.theme.inc Returns HTML for a date element formatted as a Start/End combination.
theme_date_display_interval core/modules/date/date.theme.inc Returns HTML for a date element formatted as an interval.
theme_date_display_range core/modules/date/date.theme.inc Returns HTML for a date element formatted as a range.
theme_date_display_remaining core/modules/date/date.theme.inc Returns HTML for remaining message.
theme_date_display_single core/modules/date/date.theme.inc Returns HTML for a date element formatted as a single date.
theme_date_nav_title core/modules/date/date.theme.inc Theme the calendar title.
theme_date_popup core/modules/date/date.theme.inc Format a date popup element.
theme_date_select core/modules/date/date.theme.inc Returns HTML for a "date_select" element, including all child elements.
theme_date_select_element core/modules/date/date.theme.inc Returns HTML for a date select input form element.
theme_date_text core/modules/date/date.theme.inc Returns HTML for a date text element.
theme_date_textfield_element core/modules/date/date.theme.inc Returns HTML for a date textfield input form element.
theme_date_text_parts core/modules/date/date.theme.inc Returns HTML for the text/select options for date parts in a table.
theme_date_timezone core/modules/date/date.theme.inc Returns HTML for a date timezone element.
theme_date_time_ago core/modules/date/date.theme.inc Returns HTML for a date in the format 'time ago'.
theme_details core/includes/form.inc Returns HTML to wrap children in a details element.
theme_disable core/includes/theme.inc Disables a given list of themes.
theme_dropbutton_wrapper core/includes/theme.inc Provide wrapper HTML around dropbutton lists.
theme_email core/includes/form.inc Returns HTML for an email form element.
theme_enable core/includes/theme.inc Enables a given list of themes.
theme_entityreference_entity_id core/modules/entityreference/entityreference.module Theme entity_id
theme_entityreference_label core/modules/entityreference/entityreference.module Theme label.
theme_exposed_filters core/modules/system/system.theme.inc Returns HTML for an exposed filter form.
theme_feed_icon core/includes/theme.inc Returns HTML for a feed icon.
theme_field core/modules/field/field.theme.inc Returns HTML for a field.
theme_fieldset core/includes/form.inc Returns HTML for a fieldset form element and its children.
theme_field_multiple_value_form core/modules/field/field.theme.inc Returns HTML for an individual form element.
theme_field_ui_table core/modules/field_ui/field_ui.theme.inc Returns HTML for Field UI overview tables.

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