app.html

<!DOCTYPE html>
<html {{ HTML_ATTRS }}>
  <head {{ HEAD_ATTRS }}>
    {{ HEAD }}
    <!-- Import Ionicon icons & Google Fonts our Bootstrap theme relies on -->
    <link
      href="https://cdn.jsdelivr.net/npm/ionicons@2.0.1/css/ionicons.min.css"
      rel="stylesheet"
      type="text/css"
    />
    <link
      href="//fonts.googleapis.com/css?family=Titillium+Web:700|Source+Serif+Pro:400,700|Merriweather+Sans:400,700|Source+Sans+Pro:400,300,600,700,300italic,400italic,600italic,700italic"
      rel="stylesheet"
      type="text/css"
    />
    <!-- Import the custom Bootstrap 4 theme from our hosted CDN -->
    <!-- <link rel="stylesheet" href="//demo.productionready.io/main.css"> -->
    <link rel="stylesheet" href="/index.css" />
  </head>
  <body {{ BODY_ATTRS }}>
    {{ APP }}
  </body>
</html>