Improve issue history dialog and make poster can delete their own history (#27323)

Fix #27313 (see the comment)

And some UI improvements:

### Before


![image](https://github.com/go-gitea/gitea/assets/2114189/420a314d-8f34-4e30-a557-f41cf4f0d2f2)


![image](https://github.com/go-gitea/gitea/assets/2114189/60ca0be4-b55e-4e65-be73-fd53e0d4fc36)


### After


![image](https://github.com/go-gitea/gitea/assets/2114189/d354f815-5a0c-4e63-8d59-d03ed344dbea)


![image](https://github.com/go-gitea/gitea/assets/2114189/6ef437a4-aa6f-4917-a260-00625ee71e79)


![image](https://github.com/go-gitea/gitea/assets/2114189/9d88a36c-616b-4dc9-8c6b-76adaad8acf6)

2 files changed, 8 insertions, 1 deletions

diff --git a/web_src/css/modules/modal.css b/web_src/css/modules/modal.css
index 96bc8be898..54a4ef81ca 100644
--- a/web_src/css/modules/modal.css
+++ b/web_src/css/modules/modal.css
@@ -3,13 +3,18 @@
   width: fit-content;
 }
 
-.ui.modal.g-modal-confirm > .inside.close {
+.ui.modal.g-modal-confirm > .inside.close.icon {
   padding: 0;
   width: 1em;
   height: 1em;
   top: 1.2em;
 }
 
+.ui.modal > .close.icon[height="16"] {
+  top: 0.7em; /* fomantic uses absolute layout, so if we have special icon size, it needs this trick to align vertically */
+  color: var(--color-text-dark);
+}
+
 .ui.modal > .header {
   /* can't use display:flex, because some headers have space-separated elements, eg: delete branch modal */
   color: var(--color-text-dark);
diff --git a/web_src/css/repo.css b/web_src/css/repo.css
index b7b14f7407..8e751ef88e 100644
--- a/web_src/css/repo.css
+++ b/web_src/css/repo.css
@@ -2578,12 +2578,14 @@ tbody.commit-list {
 
 .comment-diff-data {
   background: var(--color-code-bg);
+  min-height: 12em;
   max-height: calc(100vh - 10.5rem);
   overflow-y: auto;
 }
 
 .comment-diff-data pre {
   line-height: 18px;
+  margin: 1em;
   white-space: pre-wrap;
   word-break: break-all;
   overflow-wrap: break-word;