Set opaque background on markup and images (#23578)

- Set opaque background on markup images so they can visually break
`<hr>`
- Change padding of comment box so `padding` is provided by the
`.markup` element instead of its parent, matching the file rendering
view which does the same.

Before:
<img width="243" alt="Screenshot 2023-03-19 at 19 22 03"
src="https://user-images.githubusercontent.com/115237/226198663-8ff4d940-6a15-452d-ac58-14485b37fbc7.png">

After:
<img width="261" alt="Screenshot 2023-03-19 at 19 23 26"
src="https://user-images.githubusercontent.com/115237/226198689-1bf56561-4726-46dc-b583-423d65e1e13a.png">
<img width="263" alt="image"
src="https://user-images.githubusercontent.com/115237/226199002-e93c817d-6d9c-4b98-bad8-0aa0bd45b62f.png">

Example documents:

https://try.gitea.io/silverwind/symlink-test/src/branch/master/test-page.md
https://github.com/silverwind/symlink-test/blob/master/test-page.md

1 files changed, 10 insertions, 0 deletions

diff --git a/web_src/css/features/dropzone.css b/web_src/css/features/dropzone.css
index 0ce067ef30..16b3faf737 100644
--- a/web_src/css/features/dropzone.css
+++ b/web_src/css/features/dropzone.css
@@ -51,3 +51,13 @@
 .dropzone .dz-preview:hover .dz-image img {
   filter: opacity(0.5) !important;
 }
+
+.dropzone-attachments .divider {
+  margin-top: 0 !important;
+  margin-bottom: 0 !important;
+}
+
+.dropzone-attachments .grid,
+.dropzone-attachments .thumbnails {
+  padding: .5rem 1rem;
+}