fix: resolve issue with underline not displaying in input field (#6694)

#### What type of PR is this?

/area ui
/kind bug
/milestone 2.20.x

#### What this PR does / why we need it:

修复部分设备或者浏览器下，输入框中的下划线可能无法正常显示的问题。

before:

<img width="678" alt="image" src="https://github.com/user-attachments/assets/11a34729-3bed-4898-b222-0027ac71830d">

after:

<img width="681" alt="image" src="https://github.com/user-attachments/assets/8065c36a-6c94-4ac9-b859-8369dcb7d1e3">


#### Which issue(s) this PR fixes:

Fixes #5651 

#### Does this PR introduce a user-facing change?

```release-note
修复部分设备或者浏览器下，输入框中的下划线可能无法正常显示的问题。
```

ui/src/formkit/theme.ts

@@ -2,9 +2,8 @@ const textClassification = {
   label: "block text-sm font-medium text-gray-700 formkit-invalid:text-red-500",
   wrapper: "flex flex-col gap-4",
   inner:
-    "inline-flex items-center w-full relative box-border border border-gray-300 formkit-invalid:border-red-500 h-9 rounded-base overflow-hidden focus-within:border-primary focus-within:shadow-sm w-full sm:max-w-lg transition-all",
-  input:
-    "bg-white resize-none w-full text-black block transition-all h-full px-3 text-sm",
+    "bg-white inline-flex items-center w-full relative box-border border border-gray-300 formkit-invalid:border-red-500 h-9 rounded-base overflow-hidden focus-within:border-primary focus-within:shadow-sm w-full sm:max-w-lg transition-all",
+  input: "resize-none w-full text-black block transition-all px-3 text-sm",
 };
 
 const boxClassification = {