Rework header bar on issue, pull requests and milestone (#24420)

- Make search bar dynamic full width via flexbox
- Make all buttons `small` so font size is the same for all elements in
the header
- Remove primary color from search field, add SVG icon like on Code tab
- Fix button vertical padding being enlarged by SVG icons

[View diff without
whitespace](https://github.com/go-gitea/gitea/pull/24420/files?diff=unified&w=1)

<img width="1226" alt="Screenshot 2023-04-29 at 11 58 53"
src="https://user-images.githubusercontent.com/115237/235296851-74848267-664f-4c1f-b94c-a1b94196ff75.png">
<img width="1219" alt="Screenshot 2023-04-29 at 11 59 39"
src="https://user-images.githubusercontent.com/115237/235296852-bcfde5ed-8658-43c2-b7e5-3ad84611e76f.png">

Mobile:
<img width="437" alt="Screenshot 2023-04-29 at 11 59 52"
src="https://user-images.githubusercontent.com/115237/235296860-99263373-7b27-4540-868c-a93e70f281ca.png">
<img width="433" alt="Screenshot 2023-04-29 at 12 00 00"
src="https://user-images.githubusercontent.com/115237/235296862-6cf64317-a864-405a-a00f-b5ab620349f5.png">

web_src/css/base.css

@@ -769,6 +769,10 @@ a.label,
   border-color: var(--color-primary);
 }
 
+.ui.action.input .button {
+  border-color: var(--color-input-border);
+}
+
 /* currently used for search bar dropdowns in repo search and explore code */
 .ui.action.input:not([class*="left action"]) > .ui.dropdown.selection {
   min-width: 10em;
@@ -778,10 +782,21 @@ a.label,
   border-right-color: transparent;
 }
 
+.ui.action.input:not([class*="left action"]) > input:hover {
+  border-right-color: transparent;
+}
+
 .ui.action.input:not([class*="left action"]) > input:focus {
   border-right-color: var(--color-primary);
 }
 
+/* fix button enlarged vertically by svg icon */
+/* TODO: change to just `.small.button:has(svg)` but may have global side effects */
+.ui.action.input .small.button:has(svg) {
+  padding-top: 7px !important;
+  padding-bottom: 7px !important;
+}
+
 .ui.menu,
 .ui.vertical.menu {
   background: var(--color-menu);
@@ -830,6 +845,10 @@ a.label,
   color: var(--color-text-light-3);
 }
 
+.ui.menu .item::before {
+  background: var(--color-secondary);
+}
+
 /* sub menu of vertical menu */
 .ui.vertical.menu .item .menu .item {
   color: var(--color-text-light-2);

web_src/css/index.css

@@ -32,6 +32,7 @@
 @import "./repository.css";
 @import "./repository/release-tag.css";
 @import "./repository/issue-label.css";
+@import "./repository/list-header.css";
 @import "./editor.css";
 @import "./editor/combomarkdowneditor.css";
 @import "./organization.css";

web_src/css/repository.css

@@ -161,7 +161,7 @@
 
 .repository .ui.tabs.divider {
   margin-top: -1px;
-  margin-bottom: 20px;
+  margin-bottom: 12px;
 }
 
 .repository #clone-panel #repo-clone-url {
@@ -3289,18 +3289,6 @@ td.blob-excerpt {
   .repository.file.list #repo-files-table .commit-list span.commit-summary {
     display: none !important;
   }
-  .issue-list-headers.ui[class].grid > div:nth-child(1) {
-    order: 1;
-    width: 50%;
-  }
-  .issue-list-headers.ui[class].grid > div:nth-child(2) {
-    order: 3;
-    width: 100%;
-  }
-  .issue-list-headers.ui[class].grid > div.column:not(.row):nth-child(3) {
-    order: 2;
-    width: 50%;
-  }
   .repository.view.issue .comment-list .timeline,
   .repository.view.issue .comment-list .timeline-item {
     margin-left: 0;

web_src/css/repository/list-header.css

@@ -0,0 +1,36 @@
+.list-header {
+  display: flex;
+  align-items: center;
+  flex-wrap: wrap;
+  gap: .5rem;
+}
+
+.list-header-sort {
+  display: flex;
+  align-items: center;
+  justify-content: flex-end;
+  padding-left: 1rem;
+  padding-right: 1rem;
+}
+
+.list-header-search {
+  display: flex;
+  flex: 1;
+  align-items: center;
+  flex-wrap: wrap;
+  justify-content: center;
+  min-width: 200px; /* to enable flexbox wrapping on mobile */
+}
+
+.list-header-search .input {
+  flex: 1;
+}
+
+.small-pill-buttons {
+  min-height: 35.4px !important; /* match .small.button in height */
+}
+
+.small-pill-buttons .item {
+  padding-top: 6px !important;
+  padding-bottom: 6px !important;
+}