Remove background on user dashboard filter bar (#24779)

Was only an issue on arc-green:

### Before
<img width="313" alt="Screenshot 2023-05-17 at 23 33 15"
src="https://github.com/go-gitea/gitea/assets/115237/0f6916c6-c6c3-43c8-84cc-24b0a9800a43">

### After
<img width="310" alt="Screenshot 2023-05-17 at 23 32 52"
src="https://github.com/go-gitea/gitea/assets/115237/207d3d7f-ce6f-4170-b426-e743be760185">

Co-authored-by: Giteabot <[email protected]>

Author: silverwind

templates/user/dashboard/issues.tmpl

@@ -4,7 +4,7 @@
 	<div class="ui container">
 		<div class="ui stackable grid">
 			<div class="four wide column">
-				<div class="ui secondary vertical filter menu">
+				<div class="ui secondary vertical filter menu gt-bg-transparent">
 					<a class="{{if eq .ViewType "your_repositories"}}ui basic primary button{{end}} item" href="{{.Link}}?type=your_repositories&repos=[{{range $.RepoIDs}}{{.}}%2C{{end}}]&sort={{$.SortType}}&state={{.State}}">
 						{{.locale.Tr "home.issues.in_your_repos"}}
 						<strong class="ui right">{{CountFmt .IssueStats.YourRepositoriesCount}}</strong>

templates/user/dashboard/milestones.tmpl

@@ -4,7 +4,7 @@
 	<div class="ui container">
 		<div class="ui stackable grid">
 			<div class="four wide column">
-				<div class="ui secondary vertical filter menu">
+				<div class="ui secondary vertical filter menu gt-bg-transparent">
 					<a class="item" href="{{.Link}}?type=your_repositories&sort={{$.SortType}}&state={{.State}}&q={{$.Keyword}}">
 						{{.locale.Tr "home.issues.in_your_repos"}}
 						<strong class="ui right">{{.Total}}</strong>

web_src/css/helpers.css

@@ -113,6 +113,7 @@ Gitea's private styles use `g-` prefix.
 .gt-bg-brown { background: var(--color-brown) !important; }
 .gt-bg-grey { background: var(--color-grey) !important; }
 .gt-bg-gold { background: var(--color-gold) !important; }
+.gt-bg-transparent { background: transparent !important; }
 
 .gt-text-white { color: var(--color-white) !important; }