:root{--blue: #2c5aa0;--blue-dark: #1e3f73;--green: #5a8f3c;--green-soft: #eaf3e0;--bg: #f6f8fb;--card: #ffffff;--text: #1f2933;--muted: #6b7785;--border: #e3e8ef;--red: #d6453d;--amber: #e0a000;--amber-soft: #fdf6e3;--radius: 14px;--shadow: 0 2px 8px rgba(20, 40, 80, .06), 0 8px 24px rgba(20, 40, 80, .05)}*{box-sizing:border-box}html,body{margin:0;padding:0}body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,sans-serif;background:var(--bg);color:var(--text);line-height:1.55;-webkit-font-smoothing:antialiased}a{color:var(--blue);text-decoration:none}a:hover{text-decoration:underline}main{min-height:calc(100vh - 200px)}.container{max-width:1080px;margin:0 auto;padding:28px 20px 56px}.container.narrow{max-width:680px}.muted{color:var(--muted)}.small{font-size:.85rem}.center{text-align:center}.mono{font-family:ui-monospace,SF Mono,Menlo,monospace;font-size:.9rem}.page-title{font-size:1.7rem;margin:0 0 20px;color:var(--blue-dark)}.section-title{font-size:1.2rem;margin:32px 0 14px;color:var(--blue-dark)}.nav{background:var(--card);border-bottom:1px solid var(--border);position:sticky;top:0;z-index:50}.nav-inner{max-width:1180px;margin:0 auto;padding:0 20px;display:flex;align-items:center;gap:18px;height:62px}.brand{display:flex;align-items:center;gap:10px;font-weight:700;color:var(--blue-dark);font-size:1.1rem}.brand:hover{text-decoration:none}.brand small{color:var(--green);font-weight:700}.brand-logo{background:var(--blue);color:#fff;width:34px;height:34px;border-radius:9px;display:grid;place-items:center;font-size:.85rem;letter-spacing:.5px}.nav-links{display:flex;align-items:center;gap:4px;flex:1}.nav-links a{color:var(--text);padding:8px 12px;border-radius:8px;font-size:.95rem}.nav-links a:hover{background:var(--bg);text-decoration:none}.nav-links a.active{color:var(--blue);background:#eef3fb;font-weight:600}.nav-spacer{flex:1}.nav-user{display:flex;align-items:center;gap:10px}.nav-toggle{display:none;background:none;border:none;font-size:1.5rem;cursor:pointer}.btn{display:inline-flex;align-items:center;justify-content:center;gap:6px;border:1px solid transparent;border-radius:10px;padding:9px 16px;font-size:.95rem;font-weight:600;cursor:pointer;transition:.15s;background:#eef2f7;color:var(--text)}.btn:hover{filter:brightness(.97)}.btn-lg{padding:12px 22px;font-size:1rem}.btn-primary{background:var(--blue);color:#fff}.btn-ghost{background:transparent;border-color:var(--border)}.btn-success{background:var(--green);color:#fff}.btn-danger{background:var(--red);color:#fff}.btn.block{width:100%;margin-top:12px}.btn:disabled{opacity:.55;cursor:not-allowed}.row-gap{display:flex;gap:10px;margin-top:12px}.hero{text-align:center;padding:30px 0 36px}.hero h1{font-size:2.5rem;margin:0 0 12px;color:var(--blue-dark)}.hero .accent{color:var(--green)}.lead{font-size:1.12rem;color:var(--muted);max-width:640px;margin:0 auto 24px}.hero-actions{display:flex;gap:12px;justify-content:center}.grid-cards{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:16px}.feature-card{background:var(--card);border:1px solid var(--border);border-radius:var(--radius);padding:22px;box-shadow:var(--shadow);transition:.18s;display:block}.feature-card:hover{transform:translateY(-3px);text-decoration:none;border-color:#cdd9ea}.feature-icon{font-size:1.9rem}.feature-card h3{margin:10px 0 6px;color:var(--blue-dark);font-size:1.12rem}.feature-card p{margin:0;font-size:.92rem}.tabs{display:flex;gap:6px;flex-wrap:wrap;margin-bottom:18px;border-bottom:1px solid var(--border)}.tab{background:none;border:none;padding:10px 14px;cursor:pointer;font-size:.95rem;color:var(--muted);border-bottom:2px solid transparent;margin-bottom:-1px}.tab.active{color:var(--blue);font-weight:600;border-bottom-color:var(--blue)}.toolbar{display:flex;gap:10px;align-items:center;margin-bottom:16px;flex-wrap:wrap}.input{width:100%;border:1px solid var(--border);border-radius:10px;padding:10px 12px;font-size:.95rem;background:#fff;font-family:inherit}.input:focus{outline:none;border-color:var(--blue);box-shadow:0 0 0 3px #2c5aa01f}.search{flex:1;min-width:200px}.select{width:auto;min-width:180px}.textarea{resize:vertical;margin-bottom:12px}.table-wrap{background:var(--card);border:1px solid var(--border);border-radius:var(--radius);overflow:hidden;box-shadow:var(--shadow)}.data-table{width:100%;border-collapse:collapse;background:var(--card)}.data-table th{background:var(--blue-dark);color:#fff;text-align:left;padding:11px 14px;font-size:.85rem;font-weight:600}.data-table td{padding:10px 14px;border-top:1px solid var(--border);vertical-align:top;font-size:.94rem}.data-table tbody tr:nth-child(2n){background:#fafbfd}.ipa{color:var(--green);font-size:.82rem}.ipa.big{font-size:1.1rem;display:block;margin:6px 0}.speak-btn{background:none;border:none;cursor:pointer;font-size:.9rem;padding:0 2px;opacity:.65}.speak-btn:hover{opacity:1}.fc-head{display:flex;justify-content:space-between;align-items:center;gap:12px;flex-wrap:wrap}.hint{background:var(--green-soft);border-radius:10px;padding:10px 14px;font-size:.9rem;color:#3d5e29}.fc-progress{text-align:center;color:var(--muted);margin:8px 0 14px;font-size:.9rem;display:flex;gap:8px;justify-content:center;align-items:center}.flashcard{perspective:1200px;height:280px;cursor:pointer;margin-bottom:18px}.fc-inner{position:relative;width:100%;height:100%;transition:transform .5s;transform-style:preserve-3d}.flashcard.flipped .fc-inner{transform:rotateY(180deg)}.fc-front,.fc-back{position:absolute;top:0;right:0;bottom:0;left:0;backface-visibility:hidden;background:var(--card);border:1px solid var(--border);border-radius:18px;box-shadow:var(--shadow);display:flex;flex-direction:column;align-items:center;justify-content:center;padding:24px;text-align:center}.fc-back{transform:rotateY(180deg);background:#f3f8ff}.fc-word{font-size:2.2rem;font-weight:700;color:var(--blue-dark)}.fc-meaning{color:var(--muted);margin-top:8px;font-size:1.05rem}.fc-tip{position:absolute;bottom:14px;font-size:.78rem;color:#aab4c0}.fc-back-row{display:flex;align-items:center;gap:10px;margin:6px 0;font-size:1.3rem}.fc-back-label{background:var(--blue);color:#fff;border-radius:6px;font-size:.72rem;padding:2px 8px}.fc-back-val{font-weight:600}.fc-back-val.big{font-size:1.6rem;color:var(--blue-dark)}.fc-actions{display:flex;gap:12px;justify-content:center}.fc-actions .btn{flex:1;max-width:200px}.fc-finish{text-align:center;background:var(--card);border:1px solid var(--border);border-radius:var(--radius);padding:40px 20px;box-shadow:var(--shadow)}.fc-finish h2{color:var(--blue-dark)}.score-big{font-size:3rem;font-weight:800;color:var(--green);margin:10px 0}.badge{background:#eef2f7;color:var(--muted);border-radius:20px;padding:2px 10px;font-size:.75rem}.badge-new,.badge-ok{background:var(--green-soft);color:var(--green)}.badge-off{background:#fbe6e4;color:var(--red)}.quiz-card{background:var(--card);border:1px solid var(--border);border-radius:var(--radius);padding:26px;box-shadow:var(--shadow)}.quiz-label{color:var(--muted);font-size:.85rem;text-transform:uppercase;letter-spacing:.5px}.quiz-prompt{font-size:1.8rem;font-weight:700;color:var(--blue-dark);margin:8px 0 18px}.quiz-input{font-size:1.1rem;margin-bottom:12px}.quiz-options{display:grid;gap:10px}.opt{text-align:left;padding:13px 16px;border:1px solid var(--border);border-radius:10px;background:#fff;cursor:pointer;font-size:1.05rem;transition:.12s}.opt:hover:not(:disabled){border-color:var(--blue);background:#f3f8ff}.opt-correct{border-color:var(--green);background:var(--green-soft);font-weight:600}.opt-wrong{border-color:var(--red);background:#fbe6e4}.quiz-feedback{margin-top:16px;padding:12px 14px;border-radius:10px;font-size:1rem}.quiz-feedback.ok{background:var(--green-soft);color:#3d5e29}.quiz-feedback.bad{background:var(--amber-soft);color:#7a5b00}.grammar-layout{display:grid;grid-template-columns:280px 1fr;gap:20px}.lesson-list{display:flex;flex-direction:column;gap:6px;position:sticky;top:80px;align-self:start;max-height:calc(100vh - 100px);overflow-y:auto}.lesson-item{text-align:left;background:var(--card);border:1px solid var(--border);border-radius:10px;padding:10px 12px;cursor:pointer;display:flex;flex-direction:column}.lesson-item.active{border-color:var(--blue);background:#f3f8ff}.lesson-num{font-size:.75rem;color:var(--green);font-weight:700}.lesson-name{font-size:.9rem}.lesson-heading{color:var(--blue-dark);font-size:1.35rem;margin:0 0 16px}.grammar-card{background:var(--card);border:1px solid var(--border);border-radius:var(--radius);padding:20px 22px;margin-bottom:16px;box-shadow:var(--shadow)}.grammar-card h3{color:var(--blue);margin:0 0 10px}.g-meaning{margin:0 0 12px}.g-block{margin:12px 0}.g-label{display:inline-block;font-size:.72rem;font-weight:700;text-transform:uppercase;letter-spacing:.5px;color:var(--muted);margin-bottom:4px}.g-block ul{margin:4px 0;padding-left:20px}.g-block li{margin:3px 0}.g-special{background:var(--amber-soft);border-radius:10px;padding:10px 14px}.g-examples{list-style:none;padding-left:0}.g-examples li{padding:6px 0;border-bottom:1px dashed var(--border)}.g-en{color:var(--blue);font-style:italic;font-weight:500}.g-vi{color:var(--muted)}.tag-row{display:flex;gap:6px;flex-wrap:wrap;margin-top:10px}.tag{background:#eef2f7;color:var(--muted);border-radius:20px;padding:2px 10px;font-size:.72rem}.notice{background:#eef3fb;border-radius:10px;padding:12px 16px;margin:14px 0}.notice-warn{background:var(--amber-soft);color:#7a5b00}.ai-result{margin-top:20px;border:1px solid var(--border);border-radius:var(--radius);padding:20px;box-shadow:var(--shadow);background:var(--card)}.ai-result.ai-ok{border-left:4px solid var(--green)}.ai-result.ai-bad{border-left:4px solid var(--amber)}.ai-verdict{font-weight:700;font-size:1.1rem;margin-bottom:10px}.ai-corrected p{margin:4px 0 12px;font-size:1.1rem}.ai-error-item{margin:8px 0;padding:8px 0;border-top:1px dashed var(--border)}.ai-error-item .wrong{color:var(--red);text-decoration:line-through}.ai-error-item .fix{color:var(--green);font-weight:600}.ai-comment{background:var(--bg);border-radius:10px;padding:10px 14px;margin-top:12px}.stat-cards{display:grid;grid-template-columns:repeat(auto-fit,minmax(160px,1fr));gap:16px}.stat-card{background:var(--card);border:1px solid var(--border);border-radius:var(--radius);padding:22px;text-align:center;box-shadow:var(--shadow)}.stat-num{font-size:2.2rem;font-weight:800;color:var(--blue)}.stat-label{color:var(--muted);font-size:.9rem}.mastery-list{display:flex;flex-direction:column;gap:14px}.mastery-row{background:var(--card);border:1px solid var(--border);border-radius:10px;padding:12px 16px}.mastery-top{display:flex;justify-content:space-between;margin-bottom:6px}.bar{height:8px;background:#eef2f7;border-radius:6px;overflow:hidden}.bar-fill{height:100%;background:var(--green);border-radius:6px;transition:width .4s}.auth-page{display:flex;justify-content:center;padding-top:50px}.auth-card,.admin-card{background:var(--card);border:1px solid var(--border);border-radius:var(--radius);padding:30px;width:100%;max-width:420px;box-shadow:var(--shadow)}.admin-card{max-width:100%}.auth-card h1{margin:0 0 18px;color:var(--blue-dark)}.auth-card label,.admin-card label{display:block;font-size:.85rem;font-weight:600;margin:12px 0 5px}.admin-card code{background:var(--bg);padding:2px 6px;border-radius:5px}.footer{border-top:1px solid var(--border);background:var(--card);text-align:center;padding:22px;color:var(--muted);font-size:.85rem}@media (max-width: 820px){.grammar-layout{grid-template-columns:1fr}.lesson-list{flex-direction:row;overflow-x:auto;position:static;max-height:none}.lesson-item{min-width:150px}.nav-toggle{display:block}.nav-links{display:none;position:absolute;top:62px;left:0;right:0;background:var(--card);flex-direction:column;align-items:stretch;padding:10px 16px;border-bottom:1px solid var(--border);box-shadow:var(--shadow)}.nav-links.open{display:flex}.nav-spacer{display:none}.nav-user{flex-direction:column;align-items:stretch;gap:8px}}@media (max-width: 480px){.hero h1{font-size:2rem}.fc-word{font-size:1.8rem}.quiz-prompt{font-size:1.4rem}}