use https://github.com/nunocoracao/blowfish.git

themes/blowfish/assets/js/appearance.js

@@ -0,0 +1,101 @@
+const sitePreference = document.documentElement.getAttribute("data-default-appearance");
+const userPreference = localStorage.getItem("appearance");
+
+if ((sitePreference === "dark" && userPreference === null) || userPreference === "dark") {
+  document.documentElement.classList.add("dark");
+}
+
+if (document.documentElement.getAttribute("data-auto-appearance") === "true") {
+  if (
+    window.matchMedia &&
+    window.matchMedia("(prefers-color-scheme: dark)").matches &&
+    userPreference !== "light"
+  ) {
+    document.documentElement.classList.add("dark");
+  }
+  window.matchMedia("(prefers-color-scheme: dark)").addEventListener("change", (event) => {
+    if (event.matches) {
+      document.documentElement.classList.add("dark");
+    } else {
+      document.documentElement.classList.remove("dark");
+    }
+  });
+}
+
+window.addEventListener("DOMContentLoaded", (event) => {
+  const switcher = document.getElementById("appearance-switcher");
+  const switcherMobile = document.getElementById("appearance-switcher-mobile");
+
+  updateMeta();
+  this.updateLogo?.(getTargetAppearance());
+
+  if (switcher) {
+    switcher.addEventListener("click", () => {
+      document.documentElement.classList.toggle("dark");
+      var targetAppearance = getTargetAppearance();
+      localStorage.setItem(
+        "appearance",
+        targetAppearance
+      );
+      updateMeta();
+      this.updateLogo?.(targetAppearance);
+    });
+    switcher.addEventListener("contextmenu", (event) => {
+      event.preventDefault();
+      localStorage.removeItem("appearance");
+    });
+  }
+  if (switcherMobile) {
+    switcherMobile.addEventListener("click", () => {
+      document.documentElement.classList.toggle("dark");
+      var targetAppearance = getTargetAppearance();
+      localStorage.setItem(
+        "appearance",
+        targetAppearance
+      );
+      updateMeta();
+      this.updateLogo?.(targetAppearance);
+    });
+    switcherMobile.addEventListener("contextmenu", (event) => {
+      event.preventDefault();
+      localStorage.removeItem("appearance");
+    });
+  }
+});
+
+
+var updateMeta = () => {
+  var elem, style;
+  elem = document.querySelector('body');
+  style = getComputedStyle(elem);
+  document.querySelector('meta[name="theme-color"]').setAttribute('content', style.backgroundColor);
+}
+
+{{ if and (.Site.Params.Logo) (.Site.Params.SecondaryLogo) }}
+{{ $primaryLogo := resources.Get .Site.Params.Logo }}
+{{ $secondaryLogo := resources.Get .Site.Params.SecondaryLogo }}
+{{ if and ($primaryLogo) ($secondaryLogo) }}
+var updateLogo = (targetAppearance) => {
+  var elems;
+  elems = document.querySelectorAll("img.logo")
+  targetLogoPath = 
+    targetAppearance == "{{ .Site.Params.DefaultAppearance }}" ?
+    "{{ $primaryLogo.RelPermalink }}" : "{{ $secondaryLogo.RelPermalink }}"
+  for (const elem of elems) {
+    elem.setAttribute("src", targetLogoPath)
+  }
+}
+{{ end }}
+{{- end }}
+
+var getTargetAppearance = () => {
+  return document.documentElement.classList.contains("dark") ? "dark" : "light"
+}
+
+window.addEventListener("DOMContentLoaded", (event) => {
+  const scroller = document.getElementById("top-scroller");
+  const footer = document.getElementById("site-footer");
+  if(scroller && footer && scroller.getBoundingClientRect().top > footer.getBoundingClientRect().top) {
+    scroller.hidden = true;
+  }
+});