add dark mode (!)

frontend/src/App.tsx

@@ -1,4 +1,5 @@
 import './App.css'
+import { ThemeProvider } from "@/components/theme-provider"
 import LatestTemperature from "@/components/latest-temperature"
 import TemperatureHistory from "@/components/temperature-history"
 import TemperaturePlot from "@/components/temperature-plot"
@@ -9,15 +10,17 @@ import TemperaturePlot from "@/components/temperature-plot"
 
 function App() {
     return (
-        <main className="min-h-screen bg-background p-6">
-            <div className="max-w-4xl mx-auto space-y-2">
-                <TemperaturePlot />
-                <div grid grid-cols-1 md:grid-cols-1 gap-6>
-                <LatestTemperature />
-                <TemperatureHistory />
+        <ThemeProvider defaultTheme="dark" storageKey="vite-ui-theme">
+            <main className="min-h-screen bg-background p-6 w-full">
+                <div className="w-full mx-auto space-y-2">
+                    <TemperaturePlot />
+                    <div className="grid grid-cols-4 gap-6">
+                        <LatestTemperature />
+                        <TemperatureHistory />
+                    </div>
                 </div>
-            </div>
-        </main>
+            </main>
+        </ThemeProvider>
     )    
 }
 

frontend/src/components/temperature-plot.tsx

@@ -8,7 +8,7 @@ function TemperaturePlot() {
     if (error) return <p>Error: {error.message}</p>
 
     return (
-        <div>
+        <div className="w-full">
             <ResponsiveContainer width="100%" height={400}>
               <ScatterChart data={data}>
                 <XAxis dataKey="id" />

frontend/src/components/theme-provider.tsx

@@ -0,0 +1,73 @@
+import { createContext, useContext, useEffect, useState } from "react"
+
+type Theme = "dark" | "light" | "system"
+
+type ThemeProviderProps = {
+  children: React.ReactNode
+  defaultTheme?: Theme
+  storageKey?: string
+}
+
+type ThemeProviderState = {
+  theme: Theme
+  setTheme: (theme: Theme) => void
+}
+
+const initialState: ThemeProviderState = {
+  theme: "system",
+  setTheme: () => null,
+}
+
+const ThemeProviderContext = createContext<ThemeProviderState>(initialState)
+
+export function ThemeProvider({
+  children,
+  defaultTheme = "system",
+  storageKey = "vite-ui-theme",
+  ...props
+}: ThemeProviderProps) {
+  const [theme, setTheme] = useState<Theme>(
+    () => (localStorage.getItem(storageKey) as Theme) || defaultTheme
+  )
+
+  useEffect(() => {
+    const root = window.document.documentElement
+
+    root.classList.remove("light", "dark")
+
+    if (theme === "system") {
+      const systemTheme = window.matchMedia("(prefers-color-scheme: dark)")
+        .matches
+        ? "dark"
+        : "light"
+
+      root.classList.add(systemTheme)
+      return
+    }
+
+    root.classList.add(theme)
+  }, [theme])
+
+  const value = {
+    theme,
+    setTheme: (theme: Theme) => {
+      localStorage.setItem(storageKey, theme)
+      setTheme(theme)
+    },
+  }
+
+  return (
+    <ThemeProviderContext.Provider {...props} value={value}>
+      {children}
+    </ThemeProviderContext.Provider>
+  )
+}
+
+export const useTheme = () => {
+  const context = useContext(ThemeProviderContext)
+
+  if (context === undefined)
+    throw new Error("useTheme must be used within a ThemeProvider")
+
+  return context
+}