diff --git a/layouts/_default/baseof.html b/layouts/_default/baseof.html
index db3a5068..c5775991 100644
--- a/layouts/_default/baseof.html
+++ b/layouts/_default/baseof.html
@@ -3,21 +3,25 @@
 {{- end -}}
 
 <!DOCTYPE html>
-<html lang="{{ site.Language }}" dir="{{ .Language.LanguageDirection | default "auto" }}">
+{{- $theme := site.Params.defaultTheme | default "auto" }}
+{{- if eq $theme "dark" }}
+<html lang="{{ site.Language }}" dir="{{ .Language.LanguageDirection | default "auto" }}" data-theme="dark">
+{{- else if eq $theme "light" }}
+<html lang="{{ site.Language }}" dir="{{ .Language.LanguageDirection | default "auto" }}" data-theme="light">
+{{- else }}
+<html lang="{{ site.Language }}" dir="{{ .Language.LanguageDirection | default "auto" }}" data-theme="auto">
+{{- end }}
 
 <head>
     {{- partial "head.html" . }}
 </head>
 
-<body class="
-{{- if (or (ne .Kind `page` ) (eq .Layout `archives`) (eq .Layout `search`)) -}}
-{{- print "list" -}}
-{{- end -}}
-{{- if eq site.Params.defaultTheme `dark` -}}
-{{- print " dark" }}
-{{- end -}}
-" id="top">
-    {{- partialCached "header.html" . .Page -}}
+{{- if (or (ne .Kind `page` ) (eq .Layout `archives`) (eq .Layout `search`)) }}
+<body class="list" id="top">
+{{- else }}
+<body id="top">
+{{- end }}
+    {{ partialCached "header.html" . .Page -}}
     <main class="main">
         {{- block "main" . }}{{ end }}
     </main>
