Fix markdown table background (#6320)

# Motivation

Currently, there is no background in Markdown tables and pre blocks in
the light theme.

# Changes

- Different colors were used for the dark theme. These colors were also
applied to the light theme.

# Tests

- Tested locally.

| Before | <img width="1552" alt="image"
src="https://github.com/user-attachments/assets/a0042b39-5eea-4819-8383-47e07fdbdca9"
/> |
|--------|--------|
| After | <img width="1552" alt="image"
src="https://github.com/user-attachments/assets/0d78869c-5810-4218-ac98-e6725629fafb"
/> |

# Todos

- [ ] Add entry to changelog (if necessary).
Not necessary.

frontend/src/lib/components/proposal-detail/ProposalSummary.svelte

@@ -83,8 +83,8 @@
 
     :global(table),
     :global(pre) {
-      background: var(--input-background);
-      color: var(--input-background-contrast);
+      background: var(--card-background);
+      color: var(--card-background-contrast);
       border-radius: var(--border-radius);
 
       font-family:
@@ -142,12 +142,6 @@
           color: var(--primary-contrast);
         }
       }
-
-      :global(table),
-      :global(pre) {
-        background: var(--card-background);
-        color: var(--card-background-contrast);
-      }
     }
   }
 </style>