Got this in html source of every page of my blog:
<link href="/wp-content/plugins/newsletter/subscription/styles/gray.css" type="text/css" rel="stylesheet"><link href="/wp-content/plugins/newsletter/subscription/styles/widget-neutral.css" type="text/css" rel="stylesheet">
and in error.log:
2016/12/18 03:40:11 [error] 8236#8236: *62872 openat() "/wp-content/plugins/newsletter/subscription/styles/gray.css" failed (2: No such file or directory), client: IP, server: name, request: "GET /wp-content/plugins/newsletter/subscription/styles/gray.css HTTP/2.0"
2016/12/18 03:40:11 [error] 8236#8236: *62872 openat() "/wp-content/plugins/newsletter/subscription/styles/widget-neutral.css" failed (2: No such file or directory), client: IP, server: name, request: "GET /wp-content/plugins/newsletter/subscription/styles/widget-neutral.css HTTP/2.0"
How to fix it?