Improve flex ellipsis (#30479)

![image](https://github.com/go-gitea/gitea/assets/2114189/857794d8-2170-42be-a5bf-47ebacbafebd)

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Co-authored-by: silverwind <me@silverwind.io>

templates/devtest/label.tmpl

@@ -0,0 +1,27 @@
+{{template "base/head" .}}
+<link rel="stylesheet" href="{{AssetUrlPrefix}}/css/devtest.css?v={{AssetVersion}}">
+<div class="page-content devtest ui container">
+	<div>
+		<h1>Label</h1>
+		<div class="flex-text-block tw-my-2">
+			<span class="ui label">simple label</span>
+			<span class="ui red label">red label</span>
+			<span class="ui green label">green label</span>
+		</div>
+		<div class="flex-text-block tw-my-2">
+			<span class="ui basic label">basic label</span>
+			<span class="ui basic red label">basic red label</span>
+			<span class="ui basic green label">basic green label</span>
+		</div>
+		<div class="flex-text-block tw-my-2">
+			<span class="ui label">long content must be in a non-flex "gt-ellipsis" element, otherwise it won't get ellipsis. very looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong label</span>
+		</div>
+		<div class="flex-text-block tw-my-2">
+			<span class="ui label"><span class="gt-ellipsis">very looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong label</span></span>
+		</div>
+		<div class="tw-my-2">
+			<span class="ui label"><span class="gt-ellipsis">very looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong label</span></span>
+		</div>
+	</div>
+</div>
+{{template "base/footer" .}}

web_src/css/base.css

@@ -1341,6 +1341,7 @@ table th[data-sortt-desc] .svg {
   align-items: center;
   gap: .25rem;
   vertical-align: middle;
+  min-width: 0;
 }
 
 .ui.dropdown .ui.label .svg {
@@ -1357,6 +1358,7 @@ table th[data-sortt-desc] .svg {
   display: flex;
   align-items: center;
   gap: .25rem;
+  min-width: 0;
 }
 
 /* to override Fomantic's default display: block for ".menu .item", and use a slightly larger gap for menu item content */
@@ -1364,4 +1366,5 @@ table th[data-sortt-desc] .svg {
   display: flex !important;
   align-items: center;
   gap: .5rem;
+  min-width: 0;
 }

web_src/css/modules/label.css

@@ -5,6 +5,8 @@
   display: inline-flex;
   align-items: center;
   gap: .25rem;
+  min-width: 0;
+  max-width: 100%; /* since we are using "flex" to align label contents, we also need to limit the x-axis, a label shouldn't be wider than 100% */
   vertical-align: middle;
   line-height: 1;
   background: var(--color-label-bg);