CSS for Calibre on Windows (Setting the font size, background-color etc.)

calibre-user-style.css

/* 
Source: https://gist.github.com/jizusun/814c4e22ada30d8ae0a82c15b9843f8b
From: https://www.itsecmedia.com/blog/post/calibre-ebook-reader-font-smoothing/
*/

body,
body.calibre{
  font-size: 1em !important;
  font-weight: bold !important;
  font-smooth: auto;
  /* text-shadow: 0 0 4px rgba(0, 0, 0, 0.4);  */
  text-rendering: auto;
  font-family:  "华文中宋", Calibre,  Helvetica, Arial, "Segoe UI", Consolas, "Microsoft Yahei", sans-serif !important;
  margin: 0em !important;
  background-color: rgb(219, 238, 221);
}

body > div {
  margin: 1em !important;
  padding: 1em 0 !important;
}

code, pre, .pre, .program {
  font-family: Consolas, "Courier New", monospace !important;
  font-size: 1em !important;
  font-weight: 500 !important;
  font-smooth: auto;
}

div.figure {
  margin: 2em 0 !important;
}

div.note {
  padding: 1em !important;
  margin: 2em 0 !important;
}

div.list {
  margin: 1em !important;
}

Preview: