ux: 實現翻卡模式動態高度適配與版面優化

- 新增動態高度計算系統，解決翻轉時卡片大小變化問題
- 實現正面背面高度自動匹配，確保翻轉體驗一致
- 優化翻卡模式設計：移除CEFR標籤、簡化正面佈局
- 改善背面內容組織：灰底區分、左對齊文字、移除冗餘元素
- 修復背面底部空白問題，提升視覺整潔度
- 添加平滑高度過渡動畫，增強用戶體驗

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/app/learn/page.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import { useState, useEffect } from 'react'
+import { useState, useEffect, useRef, useLayoutEffect } from 'react'
 import { useRouter } from 'next/navigation'
 import { Navigation } from '@/components/Navigation'
 import AudioPlayer from '@/components/AudioPlayer'
@@ -24,6 +24,12 @@ export default function LearnPage() {
   const [reportingCard, setReportingCard] = useState<any>(null)
   const [showComplete, setShowComplete] = useState(false)
   const [quizOptions, setQuizOptions] = useState<string[]>(['brought', 'determine', 'achieve', 'consider'])
+  const [cardHeight, setCardHeight] = useState<number>(400)
+
+  // Refs for measuring card content heights
+  const cardFrontRef = useRef<HTMLDivElement>(null)
+  const cardBackRef = useRef<HTMLDivElement>(null)
+  const cardContainerRef = useRef<HTMLDivElement>(null)
 
   // Mock data with real example images
   const cards = [
@@ -70,6 +76,37 @@ export default function LearnPage() {
 
   const currentCard = cards[currentCardIndex]
 
+  // Calculate optimal card height based on content (only when card changes)
+  const calculateCardHeight = () => {
+    if (!cardFrontRef.current || !cardBackRef.current) return 400;
+
+    // Get the scroll heights to measure actual content
+    const frontHeight = cardFrontRef.current.scrollHeight;
+    const backHeight = cardBackRef.current.scrollHeight;
+
+    console.log('Heights calculated:', { frontHeight, backHeight }); // Debug log
+
+    // Use the maximum height with padding
+    const maxHeight = Math.max(frontHeight, backHeight);
+    const paddedHeight = maxHeight + 40; // Add padding for visual spacing
+
+    // Ensure minimum height for visual consistency
+    return Math.max(paddedHeight, 450);
+  };
+
+  // Update card height only when card content changes (not on flip)
+  useLayoutEffect(() => {
+    if (mounted && cardFrontRef.current && cardBackRef.current) {
+      // Wait for DOM to be fully rendered
+      const timer = setTimeout(() => {
+        const newHeight = calculateCardHeight();
+        setCardHeight(newHeight);
+      }, 50);
+
+      return () => clearTimeout(timer);
+    }
+  }, [currentCardIndex, mounted]);
+
   // Client-side mounting and quiz options generation
   useEffect(() => {
     setMounted(true)
@@ -102,6 +139,7 @@ export default function LearnPage() {
       setShowResult(false)
       setFillAnswer('')
       setShowHint(false)
+      // Height will be recalculated in useLayoutEffect
     } else {
       setShowComplete(true)
     }
@@ -115,6 +153,7 @@ export default function LearnPage() {
       setShowResult(false)
       setFillAnswer('')
       setShowHint(false)
+      // Height will be recalculated in useLayoutEffect
     }
   }
 
@@ -305,95 +344,64 @@ export default function LearnPage() {
               </button>
             </div>
 
-            <div className="card-container" onClick={handleFlip}>
+            <div
+              ref={cardContainerRef}
+              className="card-container"
+              onClick={handleFlip}
+              style={{ height: `${cardHeight}px` }}
+            >
               <div className={`card ${isFlipped ? 'flipped' : ''}`}>
                 {/* Front */}
                 <div className="card-front">
-                  <div className="bg-white rounded-xl shadow-lg p-8 text-center cursor-pointer hover:shadow-xl transition-shadow">
-                    <div className="mb-4">
-                      <span className="inline-block bg-blue-100 text-blue-800 text-xs px-2 py-1 rounded-full">
-                        {currentCard.difficulty}
-                      </span>
-                    </div>
-                    <h2 className="text-4xl font-bold text-gray-900 mb-4">
+                  <div
+                    ref={cardFrontRef}
+                    className="bg-white rounded-xl shadow-lg text-center cursor-pointer hover:shadow-xl transition-shadow"
+                  >
+                    <h2 className="text-4xl font-bold text-gray-900 mb-6">
                       {currentCard.word}
                     </h2>
-                    <p className="text-gray-600 mb-4">
-                      {currentCard.partOfSpeech} {currentCard.pronunciation}
-                    </p>
-                    <AudioPlayer text={currentCard.word} />
-                    <p className="text-sm text-gray-500 mt-4">
-                      點擊查看翻譯
-                    </p>
+                    <div className="flex items-center justify-center gap-3">
+                      <span className="text-lg text-gray-500">
+                        {currentCard.pronunciation}
+                      </span>
+                      <AudioPlayer text={currentCard.word} />
+                    </div>
                   </div>
                 </div>
 
                 {/* Back */}
                 <div className="card-back">
-                  <div className="bg-white rounded-xl shadow-lg p-8 cursor-pointer hover:shadow-xl transition-shadow">
-                    <div className="grid grid-cols-1 lg:grid-cols-2 gap-6">
-                      {/* Left Column - Text Content */}
-                      <div>
-                        <div className="mb-4">
-                          <span className="inline-block bg-blue-100 text-blue-800 text-xs px-2 py-1 rounded-full">
-                            {currentCard.difficulty}
-                          </span>
-                        </div>
-                        <h2 className="text-3xl font-bold text-gray-900 mb-2">
-                          {currentCard.word}
-                        </h2>
-                        <p className="text-lg text-blue-600 font-semibold mb-4">
-                          {currentCard.translation}
-                        </p>
-                        <p className="text-gray-600 mb-4">
-                          {currentCard.partOfSpeech} {currentCard.pronunciation}
-                        </p>
-
-                        <div className="mb-4">
-                          <AudioPlayer text={currentCard.word} />
-                        </div>
-
-                        <div className="mb-4">
-                          <h3 className="font-semibold text-gray-900 mb-2">定義</h3>
-                          <p className="text-gray-700">{currentCard.definition}</p>
-                        </div>
-
-                        <div className="mb-4">
-                          <h3 className="font-semibold text-gray-900 mb-2">例句</h3>
-                          <p className="text-gray-700 italic mb-1">"{currentCard.example}"</p>
-                          <p className="text-gray-600 text-sm">"{currentCard.exampleTranslation}"</p>
-                        </div>
-
-                        <div>
-                          <h3 className="font-semibold text-gray-900 mb-2">同義詞</h3>
-                          <div className="flex flex-wrap gap-2">
-                            {currentCard.synonyms.map((synonym, index) => (
-                              <span
-                                key={index}
-                                className="bg-gray-100 text-gray-700 px-2 py-1 rounded text-sm"
-                              >
-                                {synonym}
-                              </span>
-                            ))}
-                          </div>
-                        </div>
+                  <div
+                    ref={cardBackRef}
+                    className="bg-white rounded-xl shadow-lg cursor-pointer hover:shadow-xl transition-shadow"
+                  >
+                    {/* Content Sections */}
+                    <div className="space-y-4">
+                      {/* Definition */}
+                      <div className="bg-gray-50 rounded-lg p-4">
+                        <h3 className="font-semibold text-gray-900 mb-2 text-left">定義</h3>
+                        <p className="text-gray-700 text-left">{currentCard.definition}</p>
                       </div>
 
-                      {/* Right Column - Image */}
-                      <div className="flex items-center justify-center">
-                        <div className="relative">
-                          <img
-                            src={currentCard.exampleImage}
-                            alt={`Example for ${currentCard.word}`}
-                            className="rounded-lg shadow-md max-w-full h-auto cursor-pointer hover:shadow-lg transition-shadow"
-                            onClick={(e) => {
-                              e.stopPropagation()
-                              setModalImage(currentCard.exampleImage)
-                            }}
-                          />
-                          <div className="absolute top-2 right-2 bg-black bg-opacity-50 text-white text-xs px-2 py-1 rounded">
-                            點擊放大
-                          </div>
+                      {/* Example */}
+                      <div className="bg-gray-50 rounded-lg p-4">
+                        <h3 className="font-semibold text-gray-900 mb-2 text-left">例句</h3>
+                        <p className="text-gray-700 italic mb-2 text-left">"{currentCard.example}"</p>
+                        <p className="text-gray-600 text-sm text-left">"{currentCard.exampleTranslation}"</p>
+                      </div>
+
+                      {/* Synonyms */}
+                      <div className="bg-gray-50 rounded-lg p-4">
+                        <h3 className="font-semibold text-gray-900 mb-2 text-left">同義詞</h3>
+                        <div className="flex flex-wrap gap-2">
+                          {currentCard.synonyms.map((synonym, index) => (
+                            <span
+                              key={index}
+                              className="bg-white text-gray-700 px-3 py-1 rounded-full text-sm border border-gray-200"
+                            >
+                              {synonym}
+                            </span>
+                          ))}
                         </div>
                       </div>
                     </div>
@@ -935,7 +943,9 @@ export default function LearnPage() {
       <style jsx>{`
         .card-container {
           perspective: 1000px;
-          height: 400px;
+          transition: height 0.3s ease;
+          overflow: visible;
+          position: relative;
         }
 
         .card {
@@ -943,7 +953,7 @@ export default function LearnPage() {
           width: 100%;
           height: 100%;
           text-align: center;
-          transition: transform 0.6s;
+          transition: transform 0.6s ease;
           transform-style: preserve-3d;
         }
 
@@ -957,18 +967,34 @@ export default function LearnPage() {
           height: 100%;
           backface-visibility: hidden;
           display: flex;
-          align-items: center;
+          align-items: stretch;
           justify-content: center;
+          top: 0;
+          left: 0;
         }
 
         .card-back {
           transform: rotateY(180deg);
         }
 
-        .card-front > div, .card-back > div {
+        .card-front > div {
           width: 100%;
           height: 100%;
-          overflow-y: auto;
+          display: flex;
+          flex-direction: column;
+          justify-content: center;
+          align-items: center;
+          padding: 2rem;
+          box-sizing: border-box;
+        }
+
+        .card-back > div {
+          width: 100%;
+          padding: 1.5rem;
+          box-sizing: border-box;
+          display: flex;
+          flex-direction: column;
+          justify-content: flex-start;
         }
       `}</style>
     </div>