Add a default style if no Featured image is selected

You can test if the $thumb has any contents and then apply a class to the featured image block that you can use to hide the container.

<?php
    $thumb = wp_get_attachment_image_src(
        get_post_thumbnail_id($post->ID),
        'full'
    );
?>

<div id="post" class="featured-image <?php echo empty($thumb) ? 'no-featured-image-class' : ''; ?>" style="background-image: url('<?php echo $thumb['0']; ?>')">

Related Posts:

  1. WordPress loop specific thumbnail size
  2. How to scale image with equal width and height without distortion?
  3. How to stop featured image thumbnail [set as background image] on blog index page just repeating same image across all posts
  4. height should be set to auto to avoid pixelation in the post thumbnail function
  5. featured post as div background
  6. Adding first / last CSS classes to menus
  7. What’s the best way to use the Featured Image for responsive web design?
  8. WordPress Admin Bar pushed Sticky Footer off the bottom of the page
  9. Adding Featured Image to Post programatically
  10. “wp_enqueue_style();” don’t load new edited style
  11. How to add a featured image to a existing post via php?
  12. functions.php not adding css to website?
  13. if file_exists not working with wp_enqueue_style
  14. Using PHP to toggle stylesheet and header image, set in cookie
  15. Archive dropdown styling not applied
  16. Different background-image by category
  17. Add a Different CSS Class Into The Body Tag of Different WP Pages
  18. How can I show the post thumbnail from the most recent of a certain post type, in widget?
  19. How can I add pagination and how can I change thumbnail size?
  20. How Display Posts on category
  21. Slider loading issue
  22. Parent theme CSS overriding child CSS rules
  23. How to style options page in dashboard?
  24. Theme Options Page – User Updates Logo
  25. Dynamic Stylesheet loads but doesn’t finish
  26. How to add date to navigation bar
  27. Is it possible to use Data URI image to set a post thumbnail?
  28. Incorrect MIME type for assets with Valet
  29. Display custom post type title as text if post thumbnail is not available
  30. Customize position of social icons in upme plugin [closed]
  31. Css loads very slow [closed]
  32. How create a Shortcode with hover and complex options
  33. WordPress Multiple Navigation bars
  34. Which is the correct way to conditionally enqueue a CSS file?
  35. Use PHP in stylesheet to specify a background image based on Category ID
  36. ‘Post-thumbnails’ feature does not seem to register
  37. WordPress wp_add_inline_style unable to give hex colors?
  38. How to make container class in PHP
  39. How to create table in wordpress without plugin? [closed]
  40. Add class to DIV depending on page loaded
  41. Liking a facebook page from wordpress website?
  42. trouble with page_id & highlighting current page
  43. wordpress admin plugin menu custom css
  44. Automatically add images to a menu
  45. Where can I find the inline-css of my theme header?
  46. Website completely messes up when logging out
  47. Issue Enqueueing WordPress style.css
  48. Error display post thumbnails for previous and next post
  49. Fallback image URL if no featured image exists via a shortcode function
  50. How to add new CSS file to new PHP file
  51. Applying CSS on PHP variable [closed]
  52. Get the alt text of the image in a array
  53. Timber right sidebar in WordPress theme
  54. How to find which .mo file is responsible for displaying a particular localized string?
  55. How to Remove Theme Style CSS inside Custom Plugin?
  56. Add other class content with reference class value
  57. Add Featured Image to Existing Post
  58. Adding Custom css file in the wp-uploads directory with custom php functions
  59. Replace background image with post thumbnail in shortcode
  60. Resize post thumbnail
  61. How to hide a div section when user is logged in, in single product woocommerce
  62. How do I integrate vanilla Javascript to a wordpress website?
  63. Cannot dequeue Elementor Font Awesome css
  64. How to find and delete a menu item in php?
  65. WordPress Slider is not working
  66. How to display post meta bellow every posts
  67. Add my footer menu to the header
  68. Add Shortcode to ::before class
  69. Fix hover images blink
  70. Blog Image and Title in Right Sidebar
  71. Thumbnail wouldn’t scale to size properly
  72. Displaying POST content with HTML tags and all
  73. How to add Open/Close Toggle button into Twenty Fifteen theme for hiding left sidebar?
  74. Position a repeated article blocks
  75. Custom Thumbnails [closed]
  76. Custom Theme, Editor won’t wrap text (i.e. change width)
  77. Can’t put a hyperlink on Featured Post’s Image
  78. How to correctly add the featured immage (thumbnails) support in a WP theme? Why I can’t add a featured immage?
  79. Revision History for Entire WordPress Site
  80. wp add inline style in loop
  81. Post Thumbnail on Single (if elseif else)
  82. Display pages from specific page template
  83. the_post_thumbnail unless video id is added
  84. How do I use CSS or PHP to customize WordPress Form Manager Plugin Table?
  85. Sidebar doesnt get updated?
  86. How to NOT override inline css rules
  87. Add CSS class to PHP Statement
  88. How to add margin underneath woocommerce total price amount -> productpages
  89. Load files content [closed]
  90. Load slideshow.css file only if Slideshow is checked / on
  91. add if statement to the featured image
  92. Predefine Magazine Style Layouts
  93. It’s not showing full content for posts pages in wordpress “[…]” while customing some changes in the style.css file [closed]
  94. Add a “Next Post” & “Previous Post” styled button manually to a post
  95. Sorting Problem
  96. Custom HTML/CSS Theme into WordPress – SEO considerations
  97. Generate and upload screenshot as featured image for user-submitted post
  98. WooCommerce Checkout Cart [closed]
  99. why css file not link?how to create permalink?
  100. Using Featured Image as Hero Background in Word Press