*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
:root{
  --primary:#2563eb;--primary-dark:#1d4ed8;--primary-light:#dbeafe;
  --primary-50:#eff6ff;
  --accent:#f59e0b;--accent-dark:#d97706;
  --bg:#f8fafc;--surface:#fff;--surface-alt:#f1f5f9;
  --text:#0f172a;--text-muted:#64748b;--text-light:#94a3b8;
  --border:#e2e8f0;--shadow:0 1px 3px rgba(0,0,0,.06),0 1px 2px rgba(0,0,0,.04);
  --shadow-md:0 4px 6px -1px rgba(0,0,0,.07),0 2px 4px -2px rgba(0,0,0,.05);
  --shadow-lg:0 10px 25px -3px rgba(0,0,0,.08),0 4px 6px -4px rgba(0,0,0,.04);
  --radius:8px;--radius-lg:12px;--radius-xl:16px;
  --success:#10b981;--danger:#ef4444;--warning:#f59e0b;
  --font:-apple-system,BlinkMacSystemFont,'Inter','Segoe UI',system-ui,sans-serif;
}
html{font-size:16px;scroll-behavior:smooth}
body{font-family:var(--font);background:var(--bg);color:var(--text);line-height:1.6;min-height:100vh;-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale}
a{color:var(--primary);text-decoration:none;transition:color .15s}
a:hover{color:var(--primary-dark)}
img{max-width:100%;display:block}
::selection{background:var(--primary-light);color:var(--primary-dark)}

/* ── NAV ── */
.navbar{background:var(--surface);border-bottom:1px solid var(--border);padding:0 1.5rem;display:flex;align-items:center;justify-content:space-between;position:sticky;top:0;z-index:100;height:56px;box-shadow:var(--shadow)}
.nav-brand{font-size:1.2rem;font-weight:700;color:var(--primary);display:flex;align-items:center;gap:.5rem;letter-spacing:-.02em}
.nav-brand span{font-size:1.35rem}
.nav-links{display:flex;gap:.125rem;align-items:center}
.nav-links a{padding:.45rem .9rem;border-radius:var(--radius);font-size:.875rem;font-weight:500;color:var(--text-muted);transition:all .15s}
.nav-links a:hover{background:var(--surface-alt);color:var(--text);text-decoration:none}
.nav-links a.active{background:var(--primary-light);color:var(--primary);text-decoration:none}
.nav-user{display:flex;align-items:center;gap:.75rem}
.nav-avatar{width:32px;height:32px;border-radius:50%;background:linear-gradient(135deg,var(--primary),#7c3aed);color:#fff;display:flex;align-items:center;justify-content:center;font-weight:600;font-size:.8rem;box-shadow:0 0 0 2px var(--surface),0 0 0 3px var(--border)}
.hamburger{display:none;background:none;border:none;font-size:1.3rem;cursor:pointer;color:var(--text);padding:.25rem}

/* ── AUTH ── */
.auth-container{min-height:100vh;display:flex;align-items:center;justify-content:center;padding:1.5rem;background:linear-gradient(135deg,#0f172a 0%,#1e3a5f 30%,#2563eb 60%,#7c3aed 100%)}
.auth-container::before{content:'';position:fixed;inset:0;background:url("data:image/svg+xml,%3Csvg width='60' height='60' xmlns='http://www.w3.org/2000/svg'%3E%3Cpath d='M30 0v60M0 30h60' stroke='%23ffffff' stroke-width='.3' opacity='.05'/%3E%3C/svg%3E");pointer-events:none}
.auth-card{background:var(--surface);border-radius:var(--radius-xl);padding:2.5rem;width:100%;max-width:400px;box-shadow:0 20px 60px rgba(0,0,0,.2);position:relative;animation:authIn .4s ease}
@keyframes authIn{from{opacity:0;transform:translateY(12px)}to{opacity:1;transform:none}}
.auth-card h1{font-size:1.5rem;font-weight:700;margin-bottom:.25rem;letter-spacing:-.02em}
.auth-card p.subtitle{color:var(--text-muted);margin-bottom:1.75rem;font-size:.9rem}
.auth-card .logo{text-align:center;margin-bottom:1.25rem;font-size:2.25rem}

.form-group{margin-bottom:1rem}
.form-group label{display:block;font-size:.8rem;font-weight:600;margin-bottom:.3rem;color:var(--text);text-transform:uppercase;letter-spacing:.03em}
.form-group input,.form-group select,.form-group textarea{width:100%;padding:.625rem .875rem;border:1.5px solid var(--border);border-radius:var(--radius);font-size:.9rem;font-family:var(--font);transition:all .15s;background:var(--surface);color:var(--text)}
.form-group input:focus,.form-group select:focus,.form-group textarea:focus{outline:none;border-color:var(--primary);box-shadow:0 0 0 3px var(--primary-light)}
.form-group input::placeholder{color:var(--text-light)}
.form-group textarea{resize:vertical;min-height:80px}
.form-error{color:var(--danger);font-size:.78rem;margin-top:.25rem;display:none}
.form-group.error input,.form-group.error select{border-color:var(--danger)}
.form-group.error .form-error{display:block}

.btn{display:inline-flex;align-items:center;justify-content:center;gap:.4rem;padding:.625rem 1.25rem;border:none;border-radius:var(--radius);font-size:.9rem;font-weight:600;font-family:var(--font);cursor:pointer;transition:all .15s;position:relative}
.btn:active{transform:scale(.98)}
.btn-primary{background:var(--primary);color:#fff;box-shadow:0 1px 2px rgba(37,99,235,.3)}
.btn-primary:hover{background:var(--primary-dark);box-shadow:0 2px 8px rgba(37,99,235,.35)}
.btn-secondary{background:var(--surface-alt);color:var(--text);border:1px solid var(--border)}
.btn-secondary:hover{background:var(--border)}
.btn-accent{background:var(--accent);color:#fff}
.btn-accent:hover{background:var(--accent-dark)}
.btn-danger{background:var(--danger);color:#fff}
.btn-danger:hover{background:#dc2626}
.btn-ghost{background:none;color:var(--text-muted);padding:.4rem .75rem}
.btn-ghost:hover{background:var(--surface-alt);color:var(--text)}
.btn-sm{padding:.375rem .75rem;font-size:.8rem}
.btn-block{width:100%}
.btn:disabled{opacity:.5;cursor:not-allowed}
.btn.loading{color:transparent;pointer-events:none}
.btn.loading::after{content:'';position:absolute;width:18px;height:18px;border:2px solid transparent;border-top-color:currentColor;border-radius:50%;animation:spin .5s linear infinite}
@keyframes spin{to{transform:rotate(360deg)}}
.btn.loading.btn-primary::after{border-top-color:#fff}

.auth-footer{text-align:center;margin-top:1.5rem;font-size:.875rem;color:var(--text-muted)}
.auth-divider{display:flex;align-items:center;gap:.75rem;margin:1.25rem 0;color:var(--text-light);font-size:.8rem}
.auth-divider::before,.auth-divider::after{content:'';flex:1;height:1px;background:var(--border)}

.alert{padding:.75rem 1rem;border-radius:var(--radius);margin-bottom:1rem;font-size:.875rem;display:none;animation:alertIn .2s ease}
@keyframes alertIn{from{opacity:0;transform:translateY(-4px)}to{opacity:1;transform:none}}
.alert-error{background:#fef2f2;color:#991b1b;border:1px solid #fecaca}
.alert-success{background:#f0fdf4;color:#166534;border:1px solid #bbf7d0}
.alert.show{display:block}

/* ── LAYOUT ── */
.page-container{max-width:1100px;margin:0 auto;padding:2rem 1.5rem}
.page-header{margin-bottom:2rem}
.page-header h1{font-size:1.75rem;font-weight:700;margin-bottom:.25rem;letter-spacing:-.02em}
.page-header p{color:var(--text-muted);font-size:.95rem}

.card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius-lg);padding:1.5rem;box-shadow:var(--shadow);transition:box-shadow .2s}
.card+.card{margin-top:1rem}
.card-header{display:flex;align-items:center;justify-content:space-between;margin-bottom:1rem}
.card-header h2{font-size:1.1rem;font-weight:600}

.grid{display:grid;gap:1rem}
.grid-2{grid-template-columns:repeat(2,1fr)}
.grid-3{grid-template-columns:repeat(3,1fr)}
.grid-4{grid-template-columns:repeat(4,1fr)}

.badge{display:inline-flex;align-items:center;padding:.125rem .5rem;border-radius:999px;font-size:.7rem;font-weight:600;text-transform:capitalize;letter-spacing:.02em}
.badge-beginner{background:#dcfce7;color:#166534}
.badge-intermediate{background:#dbeafe;color:#1e40af}
.badge-advanced{background:#fce7f3;color:#9d174d}
.badge-primary{background:var(--primary-light);color:var(--primary)}

.tabs{display:flex;gap:0;border-bottom:2px solid var(--border);margin-bottom:1.5rem}
.tab{padding:.55rem 1.1rem;cursor:pointer;font-size:.875rem;font-weight:500;color:var(--text-muted);border:none;background:none;border-bottom:2px solid transparent;margin-bottom:-2px;transition:all .15s;font-family:var(--font)}
.tab:hover{color:var(--text)}
.tab.active{color:var(--primary);border-bottom-color:var(--primary)}

/* ── DASHBOARD ── */
.stats-row{display:grid;grid-template-columns:repeat(auto-fit,minmax(200px,1fr));gap:1rem;margin-bottom:2rem}
.stat-card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius-lg);padding:1.25rem;text-align:center;box-shadow:var(--shadow);transition:transform .2s,box-shadow .2s}
.stat-card:hover{transform:translateY(-2px);box-shadow:var(--shadow-md)}
.stat-card .stat-value{font-size:1.75rem;font-weight:700;color:var(--primary);letter-spacing:-.02em}
.stat-card .stat-label{font-size:.8rem;color:var(--text-muted);margin-top:.15rem;text-transform:uppercase;letter-spacing:.04em}
.stat-card .stat-icon{font-size:1.35rem;margin-bottom:.35rem}

.progress-bar{height:6px;background:var(--surface-alt);border-radius:999px;overflow:hidden;margin-top:.5rem}
.progress-fill{height:100%;background:linear-gradient(90deg,var(--primary),#7c3aed);border-radius:999px;transition:width .6s ease}

.lesson-card{border:1px solid var(--border);border-radius:var(--radius-lg);padding:1.25rem;background:var(--surface);cursor:pointer;transition:all .2s;box-shadow:var(--shadow)}
.lesson-card:hover{border-color:var(--primary);box-shadow:var(--shadow-lg);transform:translateY(-3px)}
.lesson-card h3{font-size:1rem;font-weight:600;margin-bottom:.35rem;letter-spacing:-.01em}
.lesson-card p{font-size:.85rem;color:var(--text-muted);margin-bottom:.75rem;line-height:1.5}
.lesson-card .lesson-meta{display:flex;align-items:center;gap:.65rem;font-size:.78rem;color:var(--text-light)}
.lesson-card .lesson-icon{font-size:1.75rem;margin-bottom:.65rem}

/* ── LESSONS ── */
.lesson-content{max-width:720px;margin:0 auto}
.lesson-content h1{font-size:1.75rem;letter-spacing:-.02em}
.lesson-content h2{font-size:1.25rem;margin:1.75rem 0 .75rem;color:var(--primary-dark);font-weight:600}
.lesson-content h3{font-size:1.05rem;margin:1.25rem 0 .5rem}
.lesson-content p{margin-bottom:.75rem;line-height:1.75}
.lesson-content ul,.lesson-content ol{margin:0 0 .75rem 1.5rem}
.lesson-content li{margin-bottom:.4rem;line-height:1.7}
.example-box{background:var(--primary-50);border-left:3px solid var(--primary);padding:1rem 1.25rem;border-radius:0 var(--radius) var(--radius) 0;margin:1rem 0;font-size:.9rem}
.example-box .correct{color:#166534;font-weight:600}
.example-box .incorrect{color:var(--danger);text-decoration:line-through;opacity:.7}
.tip-box{background:#fefce8;border-left:3px solid var(--accent);padding:1rem 1.25rem;border-radius:0 var(--radius) var(--radius) 0;margin:1rem 0;font-size:.9rem}
.quiz-box{background:var(--surface);border:1.5px solid var(--border);border-radius:var(--radius-lg);padding:1.5rem;margin:2rem 0}
.quiz-box h3{margin-bottom:1rem;font-size:1.15rem}
.quiz-option{display:block;padding:.6rem 1rem;margin-bottom:.4rem;border:1.5px solid var(--border);border-radius:var(--radius);cursor:pointer;transition:all .15s;font-size:.9rem}
.quiz-option:hover{border-color:var(--primary);background:var(--primary-50)}
.quiz-option.selected{border-color:var(--primary);background:var(--primary-light)}
.quiz-option.correct{border-color:var(--success);background:#f0fdf4;cursor:default}
.quiz-option.wrong{border-color:var(--danger);background:#fef2f2;cursor:default}
.quiz-result{margin-top:.65rem;padding:.65rem .85rem;border-radius:var(--radius);font-weight:600;font-size:.85rem;display:none}

/* ── COMMUNITY ── */
.thread-list{display:flex;flex-direction:column;gap:.5rem}
.thread-item{display:flex;gap:1rem;padding:1rem 1.25rem;border:1px solid var(--border);border-radius:var(--radius-lg);background:var(--surface);cursor:pointer;transition:all .15s}
.thread-item:hover{border-color:var(--primary);box-shadow:var(--shadow-md)}
.thread-avatar{width:40px;height:40px;border-radius:50%;color:#fff;display:flex;align-items:center;justify-content:center;font-weight:600;flex-shrink:0;font-size:.9rem}
.thread-body{flex:1;min-width:0}
.thread-body h3{font-size:.95rem;font-weight:600;margin-bottom:.15rem}
.thread-body p{font-size:.85rem;color:var(--text-muted);white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.thread-meta{font-size:.75rem;color:var(--text-light);margin-top:.4rem;display:flex;gap:.85rem;flex-wrap:wrap}

.post{padding:1.25rem;border-bottom:1px solid var(--border)}
.post:last-child{border-bottom:none}
.post-header{display:flex;align-items:center;gap:.75rem;margin-bottom:.75rem}
.post-header .thread-avatar{width:36px;height:36px;font-size:.8rem}
.post-author{font-weight:600;font-size:.9rem}
.post-time{font-size:.78rem;color:var(--text-light)}
.post-content{font-size:.9rem;line-height:1.75}
.post-actions{margin-top:.75rem;display:flex;gap:.85rem}
.post-actions button{background:none;border:none;color:var(--text-muted);font-size:.8rem;cursor:pointer;display:flex;align-items:center;gap:.3rem;padding:.2rem .4rem;border-radius:var(--radius);transition:all .15s}
.post-actions button:hover{color:var(--primary);background:var(--primary-50)}

.new-post-form{padding:1.25rem;border-top:1px solid var(--border)}

/* ── CHAT ── */
.chat-layout{display:grid;grid-template-columns:240px 1fr;height:calc(100vh - 56px);overflow:hidden}
.chat-sidebar{background:var(--surface);border-right:1px solid var(--border);overflow-y:auto;padding:.75rem}
.chat-sidebar-title{padding:.35rem .85rem .75rem;font-size:.7rem;font-weight:700;color:var(--text-light);text-transform:uppercase;letter-spacing:.08em}
.chat-room{padding:.55rem .85rem;border-radius:var(--radius);cursor:pointer;margin-bottom:.15rem;font-size:.875rem;transition:all .15s;display:flex;align-items:center;gap:.5rem}
.chat-room:hover{background:var(--surface-alt)}
.chat-room.active{background:var(--primary-light);color:var(--primary);font-weight:600}
.chat-room .room-icon{font-size:1rem}
.chat-main{display:flex;flex-direction:column;height:100%}
.chat-header{padding:.75rem 1.25rem;border-bottom:1px solid var(--border);background:var(--surface);font-weight:600;display:flex;align-items:center;gap:.5rem;font-size:.95rem}
.chat-messages{flex:1;overflow-y:auto;padding:1rem 1.25rem;display:flex;flex-direction:column;gap:.65rem;background:var(--bg)}
.chat-message{display:flex;gap:.55rem;max-width:75%}
.chat-message.own{align-self:flex-end;flex-direction:row-reverse}
.chat-message .msg-avatar{width:30px;height:30px;border-radius:50%;display:flex;align-items:center;justify-content:center;font-weight:600;font-size:.7rem;flex-shrink:0}
.chat-message .msg-bubble{padding:.5rem .85rem;border-radius:var(--radius-lg);font-size:.875rem;line-height:1.55}
.chat-message:not(.own) .msg-avatar{background:var(--primary);color:#fff}
.chat-message:not(.own) .msg-bubble{background:var(--surface);border:1px solid var(--border)}
.chat-message.own .msg-avatar{background:var(--accent);color:#fff}
.chat-message.own .msg-bubble{background:var(--primary);color:#fff}
.msg-sender{font-size:.72rem;font-weight:600;margin-bottom:.1rem;color:var(--text-muted)}
.msg-time{font-size:.68rem;color:var(--text-light);margin-top:.15rem;text-align:right}
.chat-message.own .msg-time{color:rgba(255,255,255,.6)}
.chat-input{display:flex;gap:.5rem;padding:.75rem 1.25rem;border-top:1px solid var(--border);background:var(--surface)}
.chat-input input{flex:1;padding:.55rem .85rem;border:1.5px solid var(--border);border-radius:20px;font-size:.875rem;font-family:var(--font)}
.chat-input input:focus{outline:none;border-color:var(--primary);box-shadow:0 0 0 3px var(--primary-light)}
.chat-input .btn{border-radius:20px;padding:.55rem 1.1rem}

.online-indicator{width:7px;height:7px;border-radius:50%;background:var(--success);display:inline-block}
.online-section-title{font-size:.7rem;font-weight:700;color:var(--text-light);text-transform:uppercase;letter-spacing:.08em;padding:.5rem .85rem;margin-top:.75rem;border-top:1px solid var(--border)}

/* ── FOOTER ── */
.footer{background:var(--surface);border-top:1px solid var(--border);padding:2rem 1.5rem;margin-top:3rem}
.footer-inner{max-width:1100px;margin:0 auto;display:flex;justify-content:space-between;align-items:center;flex-wrap:wrap;gap:1rem}
.footer-brand{font-weight:700;color:var(--primary);font-size:1.05rem;display:flex;align-items:center;gap:.4rem}
.footer-links{display:flex;gap:1.5rem}
.footer-links a{color:var(--text-muted);font-size:.85rem;transition:color .15s}
.footer-links a:hover{color:var(--primary)}
.footer-copy{color:var(--text-light);font-size:.8rem;width:100%;text-align:center;margin-top:.75rem;padding-top:.75rem;border-top:1px solid var(--border)}

/* ── EMPTY STATE ── */
.empty-state{text-align:center;padding:3rem 1.5rem;color:var(--text-muted)}
.empty-state .empty-icon{font-size:2.5rem;margin-bottom:.75rem;opacity:.5}
.empty-state p{font-size:.95rem}

/* ── ANIMATIONS ── */
@keyframes fadeInUp{from{opacity:0;transform:translateY(8px)}to{opacity:1;transform:none}}
.fade-in{animation:fadeInUp .3s ease both}
.fade-in-d1{animation-delay:.05s}
.fade-in-d2{animation-delay:.1s}
.fade-in-d3{animation-delay:.15s}

/* ── RESPONSIVE ── */
@media(max-width:768px){
  .grid-2,.grid-3,.grid-4{grid-template-columns:1fr}
  .chat-layout{grid-template-columns:1fr}
  .chat-sidebar{display:none}
  .chat-sidebar.open{display:block;position:fixed;top:56px;left:0;bottom:0;width:260px;z-index:50;box-shadow:var(--shadow-lg)}
  .nav-links{display:none;position:absolute;top:100%;left:0;right:0;background:var(--surface);flex-direction:column;padding:.75rem;border-bottom:1px solid var(--border);box-shadow:var(--shadow-lg)}
  .nav-links.open{display:flex}
  .hamburger{display:block}
  .stats-row{grid-template-columns:repeat(2,1fr)}
  .page-container{padding:1.25rem 1rem}
  .auth-card{padding:2rem 1.5rem}
  .footer-inner{flex-direction:column;text-align:center}
  .footer-links{justify-content:center}
}
@media(max-width:480px){
  .stats-row{grid-template-columns:1fr}
  .thread-meta{gap:.5rem}
}