feat(前端界面): 优化格式选择下拉框

assets/webui/ofdgo.css

@@ -199,15 +199,28 @@ button:not(:disabled):hover {
 }
 
 .format-select {
+	width: 58px;
 	height: var(--control-height);
-	min-width: 64px;
-	padding: 0 7px;
+	min-width: 0;
+	padding: 0 4px;
 	border: 1px solid var(--line);
 	border-radius: 0;
 	background: #ffffff;
 	color: #1f2428;
 }
 
+.format-select:focus,
+.format-select:focus-visible {
+	border-color: var(--accent);
+	outline: 2px solid var(--accent);
+	outline-offset: 2px;
+}
+
+.format-select option:checked {
+	background-color: #e4f3ef;
+	color: var(--accent-strong);
+}
+
 .zoom-label {
 	min-width: 42px;
 	text-align: center;
@@ -936,8 +949,8 @@ body[aria-busy="true"] .viewer-panel {
 	}
 
 	.format-select {
-		min-width: 56px;
-		padding: 0 5px;
+		width: 52px;
+		padding: 0 3px;
 	}
 
 	.footer-links {