style: set scrollbar color for dark theme

src/styles.scss

@@ -85,3 +85,14 @@ textarea,
 .dark-theme.mat-app-background {
     background-color: #1d1d1d;
 }
+
+.dark-theme {
+    ::-webkit-scrollbar {
+        overflow-y: scroll;
+        background: rgb(100, 100, 100);
+    }
+
+    ::-webkit-scrollbar-thumb {
+        background-color: rgb(60, 60, 60);
+    }
+}