Fix lightbox blocking clicks on page elements

The CSS change in 39575a0 added `display: flex` to the lightbox dialog
unconditionally, which overrode the browser's default `display: none`
for closed dialogs. This made the invisible lightbox overlay intercept
all clicks on the page.

Move flexbox properties to the `&[open]` selector so they only apply
when the dialog is actually open.

Also fix typo: `innerHtml` → `innerHTML` (capital H).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/assets/stylesheets/lightbox.css

@@ -3,14 +3,11 @@
     --dialog-duration: 350ms;
     --lightbox-padding: 3vmin;
 
-    align-items: center;
     background-color: transparent;
     block-size: 100dvh;
     border: 0;
-    display: flex;
     inline-size: 100dvw;
     inset: 0;
-    justify-content: center;
     margin: auto;
     max-height: unset;
     max-width: unset;
@@ -39,6 +36,9 @@
     /* Open state */
     &[open],
     &[open]::backdrop {
+      align-items: center;
+      display: flex;
+      justify-content: center;
       opacity: 1;
 
       @starting-style {

app/javascript/controllers/lightbox_controller.js

@@ -30,7 +30,7 @@ export default class extends Controller {
 
   reset() {
     this.zoomedImageTarget.src = ""
-    this.captionTarget.innerHtml = " "
+    this.captionTarget.innerHTML = " "
     this.dispatch('closed')
   }