style: 优化特色图选择器组件的 UI 样式

src/lib/components/admin/FeaturedImagePicker.svelte

@@ -79,7 +79,7 @@
 	}
 </script>
 
-<div class="sidebar-section">
+<div class="sidebar-box">
 	<h3>特色图</h3>
 	
 	{#if cover}
@@ -137,11 +137,7 @@
 </div>
 
 <style>
-	.sidebar-section {
-		margin-bottom: 25px;
-	}
-	
-	.sidebar-section h3 {
+	.sidebar-box h3 {
 		margin: 0 0 12px 0;
 		font-size: 0.9rem;
 		font-weight: 700;
@@ -168,29 +164,38 @@
 
 	.btn-clear {
 		position: absolute;
-		top: 5px;
-		right: 5px;
-		background: #d9534f;
+		top: 8px;
+		right: 8px;
+		background: rgba(217, 83, 79, 0.9);
 		color: #fff;
-		border: 2px solid #000;
-		padding: 2px 8px;
+		border: 1px solid rgba(0, 0, 0, 0.8);
+		border-radius: 0;
+		padding: 4px 10px;
 		font-size: 0.8rem;
 		cursor: pointer;
-		font-weight: bold;
-		box-shadow: 2px 2px 0 rgba(0,0,0,1);
+		font-weight: 600;
+		backdrop-filter: blur(4px);
 	}
 	
 	.btn-clear:hover {
-		transform: translate(-1px, -1px);
-		box-shadow: 3px 3px 0 rgba(0,0,0,1);
+		background: rgba(217, 83, 79, 1);
 	}
 
 	.full-width-input {
 		width: 100%;
-		padding: 8px;
-		border: 2px solid var(--text-color);
+		padding: 10px 12px;
+		border: 1px solid rgba(0, 0, 0, 0.12);
+		background: rgba(0, 0, 0, 0.015);
 		font-family: inherit;
 		box-sizing: border-box;
+		border-radius: 0;
+		transition: border-color 0.3s ease, box-shadow 0.3s ease;
+	}
+
+	.full-width-input:focus {
+		outline: none;
+		border-color: var(--accent-color, #419b38);
+		box-shadow: 0 0 0 3px rgba(65, 155, 56, 0.08);
 	}
 
 	.upload-area label {