add base structure

assets/darkmode.js

@@ -0,0 +1,26 @@
+// Darkmode toggle
+const toggleSwitch = document.querySelector('#darkmode-toggle')
+
+const userPref = window.matchMedia('(prefers-color-scheme: light)').matches ? 'light' : 'dark'
+const currentTheme = localStorage.getItem('theme') ?? userPref
+
+if (currentTheme) {
+  document.documentElement.setAttribute('saved-theme', currentTheme);
+  if (currentTheme === 'dark') {
+    toggleSwitch.checked = true
+  }
+}
+
+const switchTheme = (e) => {
+  if (e.target.checked) {
+    document.documentElement.setAttribute('saved-theme', 'dark')
+    localStorage.setItem('theme', 'dark')
+  }
+  else {
+    document.documentElement.setAttribute('saved-theme', 'light')
+    localStorage.setItem('theme', 'light')
+  }
+}
+
+// listen for toggle
+toggleSwitch.addEventListener('change', switchTheme, false)