docs: improve styling for form submission example (#2899)

![before](https://github.com/user-attachments/assets/3936dcc6-d9f4-49e3-8b53-973a21eaadcd)

![after](https://github.com/user-attachments/assets/8abdb950-6473-4f0a-a27d-4a8b09229a57)

## Changes
- Added border and padding to the search input field for better
visibility
- Added light gray background and border to the search button for better
clickability

## Why
- The original styling makes it difficult to recognize the search input
field and button, as they appear as plain text elements without any
visual distinction.

Author: SisyphusZheng

deno.lock

@@ -53,8 +53,10 @@ export default function Page({ data }: PageProps<Data>) {
   return (
     <div>
       <form>
-        <input type="text" name="q" value={query} />
-        <button type="submit">Search</button>
+        <input type="text" name="q" value={query} class="border p-1" />
+        <button type="submit" class="ml-1 px-2 py-1 bg-gray-100 border">
+          Search
+        </button>
       </form>
       <ul>
         {results.map((name) => <li key={name}>{name}</li>)}