feat: system dark and light mode

components/main/system/SystemOverviewGrid.tsx

@@ -12,9 +12,12 @@ export const SystemOverviewGrid = ({ voltages, onOpenDetail }: Props) => {
   return (
     <div className="grid grid-cols-2 gap-4 mb-8">
       {Object.entries(voltages).map(([key, value]) => {
-        const unit = key.includes("Temp") ? "°C" : "V";
+        const unit = key.includes("Temp") ? "\u00b0C" : "V";
         return (
-          <div key={key} className="p-4 border rounded shadow">
+          <div
+            key={key}
+            className="p-4 border rounded shadow bg-white dark:bg-gray-800 border-gray-200 dark:border-gray-700 text-gray-900 dark:text-gray-100"
+          >
             <h2 className="font-semibold">{key}</h2>
             <p>
               {formatValue(value)} {unit}