:root{--text:#4b5563;--text-h:#111827;--bg:#f9fafb;--card-bg:#fff;--border:#e5e7eb;--accent:#8b5cf6;--accent-light:#a78bfa;--accent-dark:#7c3aed;--font-family:"Outfit", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif}@media (prefers-color-scheme:dark){:root{--text:#9ca3af;--text-h:#f3f4f6;--bg:#111827;--card-bg:#1f2937;--border:#374151;--accent:#a78bfa;--accent-light:#c4b5fd;--accent-dark:#8b5cf6}}*{box-sizing:border-box}body{font-family:var(--font-family);background-color:var(--bg);color:var(--text);-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale;justify-content:center;align-items:center;min-height:100dvh;margin:0;padding:0;display:flex}#root{flex-direction:column;width:100%;max-width:500px;padding:20px;display:flex}.app-header{text-align:center;margin-bottom:30px}.app-title{color:var(--text-h);margin:0 0 8px;font-size:28px;font-weight:700}.progress-text{color:var(--text);font-size:14px;font-weight:500}.flashcard-container{perspective:1500px;cursor:pointer;-webkit-user-select:none;user-select:none;-webkit-tap-highlight-color:transparent;width:100%;max-width:340px;height:500px;margin:0 auto}.flashcard-inner{text-align:center;width:100%;height:100%;transform-style:preserve-3d;border-radius:24px;transition:transform .6s cubic-bezier(.4,0,.2,1);position:relative;box-shadow:0 20px 40px #00000026,0 1px 3px #0000000d}.flashcard-container.flipped .flashcard-inner{transform:rotateY(180deg)}.flashcard-front,.flashcard-back{backface-visibility:hidden;background-color:var(--card-bg);border-radius:24px;width:100%;height:100%;position:absolute;overflow:hidden}.flashcard-front{border:1px solid var(--border);flex-direction:column;justify-content:center;align-items:center;display:flex}.image-wrapper{aspect-ratio:1;background:linear-gradient(135deg, var(--accent), var(--accent-light));border-radius:16px;width:85%;position:relative;overflow:hidden;box-shadow:0 10px 25px #00000014}.image-wrapper.fallback-bg:after{content:"🖼️";opacity:.5;font-size:64px;position:absolute;top:50%;left:50%;transform:translate(-50%,-50%)}.image-wrapper img{object-fit:cover;width:100%;height:100%;transition:opacity .3s}.hint-overlay{color:#fff;-webkit-backdrop-filter:blur(4px);letter-spacing:.5px;background:#00000080;border-radius:20px;padding:8px 16px;font-size:14px;font-weight:500;position:absolute;bottom:20px;left:50%;transform:translate(-50%)}.nav-btn{background:var(--card-bg);border:1px solid var(--border);width:44px;height:44px;color:var(--accent-dark);cursor:pointer;z-index:10;border-radius:50%;justify-content:center;align-items:center;font-size:18px;transition:all .2s;display:flex;position:absolute;top:50%;transform:translateY(-50%);box-shadow:0 4px 12px #0000001a}.nav-btn:hover{background:#fff;transform:translateY(-50%)scale(1.05);box-shadow:0 6px 16px #00000026}.nav-btn:active{transform:translateY(-50%)scale(.95)}.prev-btn{left:12px}.next-btn{right:12px}.flashcard-back{background:var(--card-bg);border:1px solid var(--border);justify-content:center;align-items:center;padding:32px;display:flex;transform:rotateY(180deg)}.text-content{flex-direction:column;gap:24px;display:flex}.english-text{color:var(--text-h);word-wrap:break-word;margin:0;font-size:42px;font-weight:700;line-height:1.1}.chinese-text{color:var(--text);margin:0;font-size:24px;font-weight:400}