Added darkmode styles and optimized class structure

Introduced dark mode styling across sections and improved CSS for better readability and maintainability. Replaced generic class names with more descriptive ones and reorganized structure for consistency. Adjusted responsive design to ensure better display on various screen sizes.

frontend/src/styles.scss

@@ -299,6 +299,12 @@ tr {
   background: #8b8a8f;
 }
 
+// Everything for darkmode
+
+.darkmodeSection {
+  background-color: var(--color-secondary);
+  transition: 0.5s background ease;
+}
 
 @media (max-width: 1150px) {
   .container {
@@ -315,5 +321,3 @@ tr {
   }
 
 }
-
-/* main css end */