Rework label colors (#24790)

Introduce `--color-label-fg`, `--color-label-bg` and
`--color-label-hover-bg`, decoupling the label styles from other color
variables. I've set the colors so that non-interactive labels like on
tabs are dark-on-light on light theme, which imho looks better than
previous light-on-dark.

In the screenshot below, the leftmost label has hover, the second one
has active.

<img width="786" alt="Screenshot 2023-05-18 at 12 48 26"
src="https://github.com/go-gitea/gitea/assets/115237/d989bb68-504a-4406-b5f6-419ed9609f90">
<img width="789" alt="Screenshot 2023-05-18 at 13 04 07"
src="https://github.com/go-gitea/gitea/assets/115237/689a281a-a2b7-45e8-a5ee-dafb7a35e105">

---------

Co-authored-by: Giteabot <teabot@gitea.io>

web_src/css/base.css

@@ -180,10 +180,13 @@
   --color-caret: var(--color-text-dark);
   --color-reaction-bg: #0000000a;
   --color-reaction-active-bg: var(--color-primary-alpha-20);
-  --color-tooltip-bg: #000000f0;
   --color-tooltip-text: #ffffff;
+  --color-tooltip-bg: #000000f0;
   --color-header-bar: #ffffff;
-  --color-label-active-bg: #d0d0d0;
+  --color-label-text: #232323;
+  --color-label-bg: #cacaca5b;
+  --color-label-hover-bg: #cacacaa0;
+  --color-label-active-bg: #cacacaff;
   --color-accent: var(--color-primary-light-1);
   --color-small-accent: var(--color-primary-light-6);
   --color-active-line: #fffbdd;
@@ -820,16 +823,6 @@ a.label,
   margin-right: 0.35em;
 }
 
-.ui.menu .item > .label {
-  background: var(--color-grey);
-}
-
-.ui.active.label {
-  background: var(--color-label-active-bg);
-  border-color: var(--color-label-active-bg);
-  color: var(--color-text-dark);
-}
-
 .ui.menu .dropdown.item:hover,
 .ui.menu a.item:hover {
   color: var(--color-text);
@@ -1976,22 +1969,32 @@ i.icon.centerlock {
 
 .ui.label {
   padding: 0.3em 0.5em;
-  background: var(--color-light);
-  color: var(--color-text-light);
+}
+
+.ui.label,
+.ui.menu .item > .label {
+  background: var(--color-label-bg);
+  color: var(--color-label-text);
+}
+
+.ui.active.label {
+  background: var(--color-label-active-bg);
+  border-color: var(--color-label-active-bg);
+  color: var(--color-label-text);
 }
 
 .ui.labels a.label:hover,
 a.ui.label:hover {
-  background: var(--color-hover);
-  border-color: var(--color-hover);
-  color: var(--color-text);
+  background: var(--color-label-hover-bg);
+  border-color: var(--color-label-hover-bg);
+  color: var(--color-label-text);
 }
 
 .ui.labels a.active.label:hover,
 a.ui.active.label:hover {
-  background: var(--color-active);
-  border-color: var(--color-active);
-  color: var(--color-text);
+  background: var(--color-label-active-bg);
+  border-color: var(--color-label-active-bg);
+  color: var(--color-label-text);
 }
 
 .ui.label > .detail .icons {

web_src/css/themes/theme-arc-green.css

@@ -165,8 +165,13 @@
   --color-caret: var(--color-text); /* should ideally be --color-text-dark, see #15651 */
   --color-reaction-bg: #ffffff12;
   --color-reaction-active-bg: var(--color-primary-alpha-40);
+  --color-tooltip-text: #ffffff;
+  --color-tooltip-bg: #000000f0;
   --color-header-bar: #2e323e;
-  --color-label-active-bg: #4c525e;
+  --color-label-text: #dfe3ec;
+  --color-label-bg: #7c84974b;
+  --color-label-hover-bg: #7c8497a0;
+  --color-label-active-bg: #7c8497ff;
   --color-accent: var(--color-primary-light-1);
   --color-small-accent: var(--color-primary-light-5);
   --color-active-line: #534d1b;