hextra/layouts/partials/head-css.html

{{ if and (not hugo.IsProduction) (eq hugo.Environment "theme")}}
  {{ $styles := resources.Get "css/styles.css" }}
  {{ $styles = $styles | resources.PostCSS (dict "inlineImports" true) }}
  <link href="{{ $styles.RelPermalink }}" rel="stylesheet" />
{{ else }}
  {{ $styles := resources.Get "css/compiled/main.css" }}
  {{ $styles = $styles | minify | fingerprint | resources.PostProcess }}
  <link rel="preload" href="{{ $styles.RelPermalink }}" as="style" />
  <link href="{{ $styles.RelPermalink }}" rel="stylesheet" integrity="{{ $styles.Data.Integrity }}" />
{{ end }}

{{ $custom := resources.Get "css/custom.css" }}
{{ $custom = $custom | minify | fingerprint }}
<link href="{{ $custom.RelPermalink }}" rel="stylesheet" integrity="{{ $custom.Data.Integrity }}" />