feat(ui): implement hover for switch (#9057)

Followup to https://codeberg.org/forgejo/forgejo/issues/6459

Preview:
- https://codeberg.org/attachments/cc12a227-c6eb-4ab5-91ad-0ef967f88c7a
- https://codeberg.org/attachments/a13c8cb6-f654-430c-a6c6-990a2a7f0911

Changes:
- hovered items now have background painted with transition
- added E2E testing: mostly for CSS logic introduced in this PR but also a bit for existing functionality
- variable --color-active is now consistently non-transparent: it already was in forgejo-dark but is now in all themes
- some code improvements in switch.css

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/9057
Reviewed-by: Beowulf <beowulf@beocode.eu>

web_src/css/modules/switch.css

@@ -1,3 +1,17 @@
+/* Copyright 2025 The Forgejo Authors. All rights reserved.
+SPDX-License-Identifier: GPL-3.0-or-later */
+
+:root .switch {
+  --switch-padding-y: .5em;
+  --switch-padding-x: 1.125em;
+}
+
+@media (pointer: coarse) {
+  :root .switch {
+    --switch-padding-y: .75em;
+  }
+}
+
 .switch {
   display: grid;
   grid-auto-flow: column;
@@ -9,27 +23,39 @@
   border-radius: var(--border-radius);
 }
 
-.switch .item {
+.switch > .item {
   display: flex;
   gap: 0.5rem;
   align-items: center;
-  padding: .5em 1.125em;
+  padding: var(--switch-padding-y) var(--switch-padding-x);
   color: var(--color-text);
   border-radius: var(--border-radius);
   text-wrap: nowrap;
+  transition: background-color 0.1s ease;
 }
 
-.switch .active.item {
+.switch > .item:hover {
+  background: var(--color-hover);
+}
+
+/* Item that has to crawl under it's active neighbor, so when it is hovered,
+there are no ugly unpainted v/^ shapes between them */
+.switch > .item:has(+ .active.item) { /* Active neighbor is next item */
+  margin-right: calc(-1 * var(--border-radius));
+  padding-right: calc(var(--switch-padding-x) + var(--border-radius));
+}
+.switch > .active.item + .item { /* Active neighbor is previous item */
+  margin-left: calc(-1 * var(--border-radius));
+  padding-left: calc(var(--switch-padding-x) + var(--border-radius));
+}
+
+.switch > .active.item {
+  z-index: 2;
+  padding-left: var(--switch-padding-x);
   background: var(--color-active);
   outline: 1px solid var(--color-input-border);
 }
 
-@media (pointer: coarse) {
-  .switch .item {
-    padding: .75em 1.125em;
-  }
-}
-
-.switch button.item {
+.switch > button.item {
   background: transparent;
 }

web_src/css/themes/theme-forgejo-light.css

@@ -240,7 +240,7 @@
   --color-light-mimic-enabled: rgba(0, 0, 0, calc(6 / 255 * 222 / 255 / var(--opacity-disabled)));
   --color-light-border: #0000001d;
   --color-hover: #e4e4e4aa;
-  --color-active: #d4d4d8aa;
+  --color-active: #e2e2e5;
   --color-menu: var(--zinc-100);
   --color-card: var(--zinc-50);
   --fancy-card-bg: var(--zinc-100);

web_src/css/themes/theme-gitea-dark.css

@@ -205,7 +205,7 @@
   --color-light-mimic-enabled: rgba(0, 0, 0, calc(40 / 255 * 222 / 255 / var(--opacity-disabled)));
   --color-light-border: #e8e8ff28;
   --color-hover: #e8e8ff19;
-  --color-active: #e8e8ff24;
+  --color-active: #393b43;
   --color-menu: #151a1e;
   --color-card: #151a1e;
   --fancy-card-bg: #14171a;

web_src/css/themes/theme-gitea-light.css

@@ -205,7 +205,7 @@
   --color-light-mimic-enabled: rgba(0, 0, 0, calc(6 / 255 * 222 / 255 / var(--opacity-disabled)));
   --color-light-border: #0000171d;
   --color-hover: #00001708;
-  --color-active: #00001714;
+  --color-active: #ebebed;
   --color-menu: #f8f9fb;
   --color-card: #f8f9fb;
   --fancy-card-bg: #ffffff;