feat: login and register, style is not ready

src/app/services/theme.service.ts

@@ -0,0 +1,34 @@
+import { Injectable } from '@angular/core';
+import { BehaviorSubject } from 'rxjs';
+
+@Injectable({ providedIn: 'root' })
+export class ThemeService {
+  private readonly darkModeSubject = new BehaviorSubject<boolean>(false);
+
+  readonly darkMode$ = this.darkModeSubject.asObservable();
+
+  initTheme(): void {
+    const savedTheme = localStorage.getItem('theme');
+    this.applyDarkMode(savedTheme === 'dark');
+  }
+
+  toggleTheme(): void {
+    this.applyDarkMode(!this.darkModeSubject.value);
+  }
+
+  setDarkMode(isDarkMode: boolean): void {
+    this.applyDarkMode(isDarkMode);
+  }
+
+  private applyDarkMode(isDarkMode: boolean): void {
+    if (isDarkMode) {
+      document.documentElement.setAttribute('data-theme', 'dark');
+      localStorage.setItem('theme', 'dark');
+    } else {
+      document.documentElement.removeAttribute('data-theme');
+      localStorage.removeItem('theme');
+    }
+
+    this.darkModeSubject.next(isDarkMode);
+  }
+}