style: markdown render

src/pages/playground/style/content-item.less

@@ -1,6 +1,14 @@
 .content-item {
   margin-bottom: 12px;
 
+  .markdown-viewer {
+    h4 {
+      margin-top: 10px;
+      margin-bottom: 10px;
+      font-size: var(--font-size-middle);
+    }
+  }
+
   &-role {
     display: flex;
     align-items: center;

src/pages/playground/style/think-content.less

@@ -1,13 +1,19 @@
 .think-wrapper {
   margin-bottom: 16px;
   color: var(--ant-color-text-tertiary);
-  border-left: 2px solid var(--ant-color-fill-secondary);
+
+  .btn-collapse {
+    margin-bottom: 8px;
+    border-radius: var(--border-radius-base);
+    width: max-content;
+    overflow: hidden;
+  }
 
   .think-content {
     white-space: pre-wrap;
-    padding: 6px 4px;
+    padding: 12px;
+    border-left: 2px solid var(--ant-color-fill-secondary);
     background-color: var(--ant-color-fill-tertiary);
     color: var(--ant-color-text-tertiary);
-    border-radius: var(--border-radius-base);
   }
 }