add theme selector to main dashboard

frontend/src/app/components/theme-selector/theme-selector.component.html

@@ -0,0 +1,6 @@
+<div [formGroup]="themeForm" class="text-small text-center ml-2">
+    <select formControlName="theme" class="custom-select custom-select-sm form-control-secondary form-control mx-auto" style="width: 160px;" (change)="changeTheme()">
+        <option value="default" i18n="theme.mempool-theme">Mempool Theme</option>
+        <option value="contrast" i18n="theme.high-contrast">High Contrast</option>
+    </select>
+</div>

frontend/src/app/components/theme-selector/theme-selector.component.ts

@@ -0,0 +1,31 @@
+import { ChangeDetectionStrategy, Component, OnInit } from '@angular/core';
+import { UntypedFormBuilder, UntypedFormGroup } from '@angular/forms';
+import { ThemeService } from '../../services/theme.service';
+
+@Component({
+  selector: 'app-theme-selector',
+  templateUrl: './theme-selector.component.html',
+  styleUrls: ['./theme-selector.component.scss'],
+  changeDetection: ChangeDetectionStrategy.OnPush
+})
+export class ThemeSelectorComponent implements OnInit {
+  themeForm: UntypedFormGroup;
+  themes = ['default', 'contrast'];
+
+  constructor(
+    private formBuilder: UntypedFormBuilder,
+    private themeService: ThemeService,
+  ) { }
+
+  ngOnInit() {
+    this.themeForm = this.formBuilder.group({
+      theme: ['default']
+    });
+    this.themeForm.get('theme')?.setValue(this.themeService.theme);
+  }
+
+  changeTheme() {
+    const newTheme = this.themeForm.get('theme')?.value;
+    this.themeService.apply(newTheme);
+  }
+}