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a) can you see in the log that the css files are being requested and served?
From access.log of the non working server (15.0): 10.47.5.102 - - [06/May/2019:11:48:47 +0200] "GET /wordpress/wp-includes/css/dist/block-library/theme.min.css?ver=5.1.1 HTTP/1.1" 200 1031 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Firefox/60.0" 10.47.5.102 - - [06/May/2019:11:48:47 +0200] "GET /wordpress/wp-includes/css/dist/block-library/style.min.css?ver=5.1.1 HTTP/1.1" 200 25242 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Firefox/60.0" 10.47.5.102 - - [06/May/2019:11:48:47 +0200] "GET /wordpress/wp-content/themes/twentynineteen/style.css?ver=1.3 HTTP/1.1" 200 212579 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Firefox/60.0" 10.47.5.102 - - [06/May/2019:11:48:47 +0200] "GET /wordpress/wp-content/themes/twentynineteen/print.css?ver=1.3 HTTP/1.1" 200 3969 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Firefox/60.0" 10.47.5.102 - - [06/May/2019:12:23:33 +0200] "GET /wordpress/wp-includes/css/dist/block-library/style.min.css?ver=5.1.1 HTTP/1.1" 200 25242 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Firefox/60.0" 10.47.5.102 - - [07/May/2019:12:33:39 +0200] "GET /wordpress/wp-includes/css/editor.min.css HTTP/1.1" 200 27128 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Firefox/60.0" The last line is result of:
b) if you request just a css file, how does it look?
https://my.server.name/wordpress/wp-includes/css/editor.min.css which results in /*! This file is auto-generated */ .mce-tinymce{box-shadow:none}.mce-container,.mce-container *,.mce-widget,.mce-widget *{color:inherit;font-family:inherit}.mce-container .mce-monospace,.mce-widget .mce-monospace{font-family:Consolas,Monaco,monospace;font-size:13px;line-height:150%}#mce-modal-block,#mce-modal-block.mce-fade{opacity:.7;filter:alpha(opacity=70);transition:none;background:#000}.mce-window{border-radius:0;box-shadow:0 3px 6px rgba(0,0,0,.3);-webkit-font-smoothing:subpixel-antialiased;transition:none}.mce-window .mce-container-body.mce-abs-layout{overflow:visible}.mce-window .mce-window-head{background:#fcfcfc;border-bottom:1px solid #ddd;padding:0;min-height:36px}.mce-window .mce-window-head .mce-title{color:#444;font-size:18px;font-weight:600;line-height:36px;margin:0;padding:0 36px 0 16px}.mce-window .mce-window-head .mce-close,.mce-window-head .mce-close .mce- ... Calling the css file directly on the 42.3 server gives the same result -> displayed as text file.
c) check encoding and filetype with Ctrl-i [>] Where? In my browser it opens the bookmarks. "file" on the server identifies css files as ASCII text
thanks Hermann-Josef Beckers