in

in/script/main.js

@@ -0,0 +1,31 @@
+const button = document.getElementById("theme");
+
+function theme_get() {
+    return document.documentElement.getAttribute("data-theme");
+}
+function theme_load() {
+    const theme = localStorage.getItem("theme");
+    if (theme) {
+        theme_set(theme);
+    }
+}
+function theme_set(theme) {
+    document.documentElement.setAttribute("data-theme", theme);
+    button.innerHTML = theme;
+    theme_write(theme);
+}
+function theme_swap(theme) {
+    return theme === "dark" ? "light" : "dark";
+}
+function theme_toggle() {
+    theme_set(theme_swap(theme_get()));
+}
+function theme_write(theme) {
+    localStorage.setItem("theme", theme);
+}
+
+button.addEventListener("click", () => {
+    theme_toggle();
+});
+
+theme_load();