feat: Add styling for keyboard keys (#2478)

Adds styling to the `<kbd>` element in Markdown.

## Preview


https://pr-2478.preview.docs.apify.com/platform/integrations/mcp#client-configuration

In light mode:
<img width="701" height="234" alt="Screenshot 2026-04-29 at 11 22 51"
src="https://github.com/user-attachments/assets/a620bf19-3bd1-4299-986d-e30a69685add"
/>

In dark mode:
<img width="694" height="217" alt="Screenshot 2026-04-29 at 11 22 34"
src="https://github.com/user-attachments/assets/0c6e15b6-b794-4747-bb73-e832be158882"
/>

Author: szaganek

apify-docs-theme/src/theme/custom.css

@@ -367,6 +367,23 @@ html[data-theme='dark'] {
     }
 }
 
+.markdown kbd {
+    background-color: white;
+    padding: 1.5px 10px;
+    border-radius: 5px;
+    border-left: 1px solid rgb(116, 116, 116);
+    border-right: 1px solid rgb(116, 116, 116);
+    border-bottom: 1.5px solid rgb(116, 116, 116);
+    box-shadow: 0 0 1px rgb(116, 116, 116);
+    color: rgb(39, 39, 39);
+    font-size: 1.5rem;
+}
+
+html[data-theme='dark'] .markdown kbd {
+    background-color: #4a4a4cd3;
+    color: rgb(255, 255, 255);
+}
+
 /* Setting the base size to 10px so it's easy to use rem for scaling (1.6rem = 16px) */
 html {
     font-size: 10px;