preserve theme selection

themes/theme.js

@@ -0,0 +1,41 @@
+async function try_load_previous_theme(){
+    if (getCookie("js_theme_selection_cookie")) {
+        theme_selection = getCookie("js_theme_selection_cookie");
+        let css = localStorage.getItem('theme-' + theme_selection);
+        if (css) {
+            change_theme(theme_selection, css);
+        }
+    }
+}
+
+async function change_theme(theme_selection, css) {
+    if (theme_selection.length==0) {
+        try_load_previous_theme();
+        return;
+    }
+
+    var existingStyles = document.querySelectorAll("body > gradio-app > div > style")
+    for (var i = 0; i < existingStyles.length; i++) {
+        var style = existingStyles[i];
+        style.parentNode.removeChild(style);
+    }
+    var existingStyles = document.querySelectorAll("style[data-loaded-css]");
+    for (var i = 0; i < existingStyles.length; i++) {
+        var style = existingStyles[i];
+        style.parentNode.removeChild(style);
+    }
+
+    setCookie("js_theme_selection_cookie", theme_selection, 3);
+    localStorage.setItem('theme-' + theme_selection, css);
+
+    var styleElement = document.createElement('style');
+    styleElement.setAttribute('data-loaded-css', 'placeholder');
+    styleElement.innerHTML = css;
+    document.body.appendChild(styleElement);
+}
+
+
+// // 记录本次的主题切换
+// async function change_theme_prepare(theme_selection, secret_css) {
+//     setCookie("js_theme_selection_cookie", theme_selection, 3);
+// }