Theme Customizer – How to create a sub panel

This slide-out panel for picking a widget or nav menu item to add is specific to the implementations of Widgets and Nav Menus in the Customizer. There is no generic facility for adding this UI feature, so I suggest looking at Core to look at how it is implemented there to copy into your plugin. For nav menus, see the AvailableMenuItemsPanelView JS and the corresponding CSS:

https://core.trac.wordpress.org/browser/tags/4.4.1/src/wp-admin/js/customize-nav-menus.js#L92
https://core.trac.wordpress.org/browser/tags/4.4.1/src/wp-admin/css/customize-nav-menus.css#L557

Related Posts:

  1. Color Options from Theme Customizer API not returning via get_theme_mod()
  2. WordPress Customazation API section in section
  3. Link to specific Customizer section
  4. When cropping a header image, retain meta data (i.e. name, description, etc.) from original image?
  5. How to refresh WordPress Customizer panel upon entering a value
  6. Looking for a way to load a function after customizer preview refresh complete
  7. Display custom_background outside wp_head()
  8. How do I change Twenty Nineteen’s primary color without using the color slider in the theme customizer?
  9. Register theme customizer settings when theme activates [duplicate]
  10. How to change the themes “Live Preview” url within the Appearance->Themes page?
  11. Two Navigation Menus – secondary nav is including main nav
  12. How to conditionally display widgetized areas in theme customizer?
  13. Create more than one section in Theme Customizer
  14. How do you approach block structured content?
  15. Own Theme Customizer displays error message when saving, saving still works
  16. Child Theme not overriding a template section on live site – but is on local site
  17. How do I remove ‘Active Theme’ section from Customizer?
  18. wordpress-theme 2017: featured image behaviour: where to set the height of the featured image?
  19. WordPress customizer extremely slow, cant work in it
  20. Dynamic image for Jumbotron on WordPress Custom Theme
  21. Issues with dynamic widget in theme customizer
  22. Theme customizer hiding sections
  23. WP Customize API Checkbox change value
  24. Warning: call_user_func() expects parameter 1 to be a valid callback
  25. Page structure using The Customizer Api
  26. WordPress Theme redirects to the Index page – Theme customizer problem
  27. What’s the best way to go from a design to a customized WordPress site?
  28. How to change background color in the Notepad++ text editor?
  29. What are all the available parameters for query_posts?
  30. Does WordPress work without a theme?
  31. Is it OK to remove theme credits from footer? [duplicate]
  32. Add a dropdown to theme customizer
  33. What theme is good for posting code? [closed]
  34. Difference between stylesheet_directory and template_directory
  35. How to see files in directories in “Edit Themes” screen
  36. WordPress generating 404 on .mp4 file in theme folder
  37. Why are my widgets not saving when being added to a sidebar?
  38. Building useful features into your theme
  39. How to remove “Proudly powered by WordPress” in Twenty Sixteen (2016) theme?
  40. Editing theme files and access to the Code pages only to super-admin?
  41. Edit theme wp_head
  42. Current theme broken – after server and domain migration
  43. Enqueue different stylesheets using IE conditionals
  44. Categories for Pages Not Saving in Admin with Custom Categories Metabox?
  45. Switch Theme Through Options Panel
  46. Weird post pagination url redirect
  47. How get Themes list via REST api?
  48. Activate a new WordPress Theme Only for Admins
  49. WordPress Fatal error: Call to undefined get_header() in index.php on line 15 [closed]
  50. Setting a static home page and blog page without using the settings
  51. Can’t Install Child Theme “The parent theme is missing. Please install the “Default” parent theme.”
  52. Can i have a single wordpress site to have two themes ( one for pc other for mobiles)
  53. Translated my theme (translation not showing up)
  54. How to use get_page_by_title() with qTranslate?
  55. Changing $before_widget for certain widgets
  56. wp theme.. Could not create directory
  57. Multi-level page hierarchy
  58. How prevent someone from opening my theme directory
  59. loss of theme options while site deployment in production
  60. How to install WordPress theme and configure it? [closed]
  61. How do I get rid of or change the footer in my child theme?
  62. Categories gone after changing theme / demos [closed]
  63. Angular integration with homepage
  64. Edited Child Theme’s “header.php” but it doesn’t appear to change the file
  65. WordPress redwaves-lite theme Comments Quote remove [closed]
  66. Page has a parent and $post->post_parent returns 0
  67. How to create different navigation for registered users in WooThemes Canvas?
  68. Selected template is not respected for home page in WordPress
  69. How to restore file or theme?
  70. A /proc folder in wp-content?
  71. how do i in ignore/disable/delete a javascript call from parent in child theme?
  72. How to install themes with the demo content?
  73. Jetpack CSS .screen-reader-text breaks mobile menu [closed]
  74. Error when using ‘continue reading’
  75. How to update theme to specific version
  76. Child theme’s stylesheet cannot load [closed]
  77. Hi everybody, I have a problem of search box
  78. Changing an image in header.php
  79. Will I lose the pages I’ve created within a default WordPress theme when adding a new theme?
  80. How to get the theme directory URI?
  81. Twenty Ten Theme: Replace the Logo by a picture without moving the code
  82. In a specific blog, the K2 theme does not have a Text Widget
  83. How to fix Scrape key check failed on WordPress VPS?
  84. Elementor Sidebar not loading when PRO elements plugin is active
  85. WordPress theme options checkbox default checked state
  86. How to show some of category in wordpress
  87. Edit a template while still keeping a Landing Page on the main address
  88. Change whole theme depending on resolution
  89. post_prev & post_next within same category
  90. Costum Theme template directoy url problem
  91. How to find out which template the HTML content comes from?
  92. What is the general cut-off date for reviewed themes in the WordPress.org repository?
  93. Include root files into header files
  94. Commenting in CSS (//) equals “none”? [closed]
  95. What is the section ID (name) for “Menus” in the Customizer?
  96. My theme is not translated
  97. Wrong theme being activated
  98. How to create an Info Box on WordPress [closed]
  99. I am unable to remove “© 2022 My Blog | PopularFX Theme ” from footer [closed]
  100. Workaround AJAX calling without directly calling WordPress backend (Admin dashboard) because it is restricted to the end user (the public)