feat: Implement Dark Mode

Added styles and configurations to enable dark mode throughout the application. The dark mode features a deep blue color scheme for primary elements and improved visibility for cursor. Selected option text in mat-select now appears in white for better contrast. This enhancement provides users with the option to switch between light and dark modes seamlessly.

Changes:
- Added dark mode styles in the theme service
- Updated mifosx-theme.scss for dark mode customization
- Adjusted cursor visibility in dark mode
- Modified selected option text color in mat-select

Fixes #2021

Implemented the black-logo image into white-logo-image dynamically

src/theme/_material-palette.scss

@@ -1,3 +1,6 @@
+
+/* ############ Light mode palettes ################*/
+
 $primary-palette: (
   100: #5ba2ec,
   500: #1074b9,
@@ -19,3 +22,27 @@ $accent-palette: (
     700: rgba(black, 0.87)
   )
 );
+
+/* ############ Dark mode palettes ################*/
+
+$dark-primary-palette: (
+  100: #273350,
+  500: #313f6b,
+  700: #39415c,
+  contrast: (
+    100: white,
+    500: rgba(white, 0.87),
+    700: rgba(white, 0.87)
+  )
+);
+
+$dark-accent-palette: (
+  100: #364461,
+  500: #3e5372,
+  700: #476385,
+  contrast: (
+    100: white,
+    500: white,
+    700: white
+  )
+);

src/theme/mifosx-theme.scss

@@ -15,6 +15,10 @@
 // Be sure that you only ever include this mixin once!
 @include mat.core();
 
+
+/* ################################## Light theme ################################### */
+
+
 // Define the palettes for your theme using the Material Design palettes available in palette.scss
 // (imported above). For each palette, you can optionally specify a default, lighter, and darker
 // hue. Available color palettes: https://material.io/design/color/
@@ -36,3 +40,51 @@ $mifosx-app-theme: mat.define-light-theme($mifosx-app-primary, $mifosx-app-accen
 @include dashboard-component-theme($mifosx-app-theme);
 @include shares-account-view-component-theme($mifosx-app-theme);
 @include account-view-component-theme($mifosx-app-theme);
+
+
+/* ################################## Dark theme ################################### */
+
+
+// Define the palettes for your theme using the Material Design palettes available in palette.scss
+$mifosx-app-dark-primary:  mat.define-palette($dark-primary-palette);
+$mifosx-app-dark-accent:  mat.define-palette($dark-accent-palette);
+$mifosx-app-dark-warn:    mat.define-palette(mat.$red-palette);
+
+// Create the theme object (a Sass map containing all of the palettes).
+$mifosx-app-dark-theme: mat.define-dark-theme($mifosx-app-dark-primary, $mifosx-app-dark-accent, $mifosx-app-dark-warn);
+
+// Include theme styles for core and each component used in your app.
+.dark-theme {
+
+    // Override the background color of the label text for dark theme
+    .mat-option-text,.mat-input-element,.mat-form-field-label{
+        color: white !important;
+    }
+    mifosx-popover,.mat-menu-content{
+        background-color: #303135;
+        color : white;
+    }
+
+    // Override the background color of the calendar for dark theme
+    .mat-calendar,
+    .mat-calendar-body-cell,
+    .mat-calendar-body-label,
+    .mat-calendar-table{
+        background-color: #303135;
+        border: none;
+    }
+    
+    // Changing the logo color for dark mode
+    .img-button,
+    .app-user-photo,
+    .profile-image{
+        filter: invert(100%);
+    }
+    
+    @include mat.all-component-themes($mifosx-app-dark-theme);
+    @include groups-view-component-theme($mifosx-app-dark-theme);
+    @include centers-view-component-theme($mifosx-app-dark-theme);
+    @include dashboard-component-theme($mifosx-app-dark-theme);
+    @include shares-account-view-component-theme($mifosx-app-dark-theme);
+    @include account-view-component-theme($mifosx-app-dark-theme);
+}