Update appearance

assets/theme.js

@@ -0,0 +1,15 @@
+const setTheme = (theme) => {
+  document.documentElement.className = theme;
+  localStorage.setItem('theme', theme);
+}
+
+document.getElementById('theme-select').addEventListener('change', function() {
+  setTheme(this.value);
+});
+
+const getTheme = () => {
+  const theme = localStorage.getItem('theme');
+  theme && setTheme(theme);
+}
+
+getTheme();