added nebular theme

src/themes.scss

@@ -0,0 +1,19 @@
+@forward '@nebular/theme/styles/theming';
+@use '@nebular/theme/styles/theming' as *;
+@use '@nebular/theme/styles/themes/cosmic';
+
+$nb-themes: nb-register-theme((
+
+  // add your variables here like:
+
+  // color-primary-100: #f2f6ff,
+  // color-primary-200: #d9e4ff,
+  // color-primary-300: #a6c1ff,
+  // color-primary-400: #598bff,
+  // color-primary-500: #3366ff,
+  // color-primary-600: #274bdb,
+  // color-primary-700: #1a34b8,
+  // color-primary-800: #102694,
+  // color-primary-900: #091c7a,
+
+), cosmic, cosmic);