chore(website): fix DocSearch button with border and transition effects (#415)

This pull request introduces a minor improvement to the
`website/.vitepress/theme/style.css` file. It enhances the styling of
the `.DocSearch-Button` element by adding a border transition effect on
hover for better user experience.

* `.DocSearch-Button` styling: Added a solid border with a transparent
default color and a smooth transition effect. The border color changes
to `var(--vp-c-brand-1)` on hover.

---------

Co-authored-by: Copilot <[email protected]>

Author: lumirlumir

website/.vitepress/theme/style.css

@@ -66,6 +66,15 @@
   --vp-home-hero-image-filter: blur(44px);
 }
 
+.DocSearch-Button {
+  border: 1px solid transparent;
+  transition: border-color 0.2s ease-in-out;
+}
+
+.DocSearch-Button:hover {
+  border-color: var(--vp-c-brand-1);
+}
+
 @media (min-width: 640px) {
   :root {
     --vp-home-hero-image-filter: blur(56px);