:root{--bg:#F7F8FA;--card:#fff;--line:#E3E6EE;--text:#14161B;--muted:#5A6070;--accent:#2F4BD8;--ok:#0F7A5C;
--warn-bg:#FFF1DE;--warn:#8A4B00;--bad-bg:#FDECEC;--bad:#9B1C1C;--r:20px}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{margin:0;background:var(--bg);color:var(--text);font:16px/1.55 Inter,system-ui,sans-serif}
h1,h2,h3,.num{font-family:Manrope,Inter,sans-serif;letter-spacing:-.02em;line-height:1.15;margin:0}
h1{font-size:clamp(32px,6vw,54px);font-weight:800}h2{font-size:clamp(26px,4vw,36px);font-weight:800}h3{font-size:19px;font-weight:700}
p{margin:0}a{color:var(--accent)}
.wrap{max-width:1120px;margin:0 auto;padding:0 20px}
.card{background:var(--card);border:1px solid var(--line);border-radius:var(--r);padding:22px}
.muted{color:var(--muted)}
.ico{width:22px;height:22px;stroke:currentColor;fill:none;stroke-width:1.6;stroke-linecap:round;stroke-linejoin:round;flex:none}
.btn{display:inline-flex;align-items:center;justify-content:center;gap:8px;min-height:44px;padding:0 22px;border-radius:999px;border:1px solid var(--line);background:#fff;color:var(--text);font:600 15px Inter,sans-serif;cursor:pointer;text-decoration:none}
.btn.primary{background:var(--accent);border-color:var(--accent);color:#fff}
.btn.ghost{background:transparent}
.btn:focus-visible,input:focus-visible,select:focus-visible,textarea:focus-visible{outline:2px solid var(--accent);outline-offset:2px}
input,select,textarea{width:100%;min-height:46px;padding:10px 16px;border:1px solid var(--line);border-radius:14px;background:#fff;font:16px Inter,sans-serif;color:var(--text)}
label{display:block;font-weight:600;font-size:14px;margin:14px 0 6px}
.seg{display:inline-flex;border:1px solid var(--line);border-radius:999px;background:#fff;padding:3px}
.seg a,.seg button{padding:6px 14px;border-radius:999px;border:0;background:none;color:var(--muted);font:600 13px Inter;text-decoration:none;cursor:pointer;min-height:32px}
.seg .on{background:var(--accent);color:#fff}
.err{background:var(--bad-bg);color:var(--bad);border-radius:14px;padding:12px 16px;margin:12px 0}
.okmsg{background:#E3F5EE;color:var(--ok);border-radius:14px;padding:12px 16px;margin:12px 0}
/* header */
.hdr{position:sticky;top:0;z-index:10;background:rgba(247,248,250,.92);backdrop-filter:blur(8px);border-bottom:1px solid var(--line)}
.hdr .wrap{display:flex;align-items:center;gap:18px;min-height:64px}
.logo{font:800 22px Manrope;color:var(--text);text-decoration:none;display:flex;align-items:center;gap:8px}
.logo i{width:28px;height:28px;border-radius:9px;background:var(--accent);display:inline-block}
.menu{display:flex;gap:22px;margin-left:auto}.menu a{color:var(--muted);text-decoration:none;font-weight:500;font-size:15px}
.hdr .right{display:flex;gap:10px;align-items:center}
@media(max-width:760px){.menu{display:none}.hdr .right{margin-left:auto}}
/* landing */
.hero{padding:56px 0 40px;display:grid;gap:32px;grid-template-columns:1.1fr .9fr;align-items:center}
@media(max-width:860px){.hero{grid-template-columns:1fr;padding:32px 0}}
.hero p.lead{font-size:18px;color:var(--muted);margin:18px 0 26px;max-width:540px}
.chat-demo{display:flex;flex-direction:column;gap:10px}
.bub{max-width:86%;padding:12px 16px;border-radius:18px;font-size:15px}
.bub.u{align-self:flex-end;background:var(--accent);color:#fff;border-bottom-right-radius:6px}
.bub.b{align-self:flex-start;background:#fff;border:1px solid var(--line);border-bottom-left-radius:6px}
section.s{padding:56px 0}
.steps{display:grid;gap:16px;grid-template-columns:repeat(3,1fr);margin-top:28px}
@media(max-width:760px){.steps{grid-template-columns:1fr}}
.step .num{width:40px;height:40px;border-radius:12px;background:#E9EDFC;color:var(--accent);display:grid;place-items:center;font-weight:800;margin-bottom:14px}
.two{display:grid;gap:24px;grid-template-columns:1fr 1fr;margin-top:28px;align-items:start}
@media(max-width:860px){.two{grid-template-columns:1fr}}
.ticks{list-style:none;padding:0;margin:0;display:grid;gap:14px}.ticks li{display:flex;gap:12px}.ticks .ico{color:var(--ok);margin-top:2px}
.pill{display:inline-block;padding:4px 12px;border-radius:999px;font-size:13px;font-weight:600}
.pill.warn{background:var(--warn-bg);color:var(--warn)}.pill.ok{background:#E3F5EE;color:var(--ok)}.pill.bad{background:var(--bad-bg);color:var(--bad)}
details{background:#fff;border:1px solid var(--line);border-radius:18px;padding:16px 20px;margin-top:12px}
summary{cursor:pointer;font-weight:600;min-height:28px}details p{margin-top:10px;color:var(--muted)}
.dark{background:#14161B;color:#fff;border-radius:28px;padding:40px;margin:20px 0 56px;display:grid;gap:28px;grid-template-columns:1fr 1fr}
@media(max-width:860px){.dark{grid-template-columns:1fr;padding:26px}}
.dark input,.dark select{background:#1F2229;border-color:#33373F;color:#fff}.dark label{color:#C9CDD8}.dark p{color:#B5BAC7}
footer{padding:28px 0 40px;color:var(--muted);font-size:14px;border-top:1px solid var(--line)}
/* login */
.center{min-height:100vh;display:grid;place-items:center;padding:20px}.box{width:100%;max-width:420px}
.tabs{display:grid;grid-template-columns:1fr 1fr;gap:6px;margin:18px 0}
/* parent */
.page{max-width:900px;margin:0 auto;padding:20px}
.grid2{display:grid;gap:16px;grid-template-columns:1fr 1fr}@media(max-width:700px){.grid2{grid-template-columns:1fr}}
.alert{background:var(--bad-bg);color:var(--bad);border:1px solid #F4C3C3;border-radius:var(--r);padding:18px 20px;display:flex;gap:14px;margin-bottom:16px}
.stat{font:800 34px Manrope}.code{font:800 34px Manrope;letter-spacing:.18em;background:#E9EDFC;color:var(--accent);padding:12px 20px;border-radius:16px;display:inline-block}
.chips{display:flex;flex-wrap:wrap;gap:8px;margin-top:10px}
.row{display:flex;gap:12px;align-items:center;flex-wrap:wrap}
.modecards{display:grid;gap:10px}.modecards label{margin:0;border:1px solid var(--line);border-radius:16px;padding:12px 14px;display:flex;gap:12px;align-items:flex-start;font-weight:500;cursor:pointer;background:#fff}
.modecards input{width:auto;min-height:0;margin-top:4px}.modecards b{display:block}.modecards span{color:var(--muted);font-size:14px}
.modecards label:has(input:checked){border-color:var(--accent);background:#F2F4FE}
/* student app */
.shell{display:grid;grid-template-columns:1fr;min-height:100vh;min-height:100dvh}
.side{display:none}
.main{padding:20px 20px 96px;max-width:800px;width:100%;margin:0 auto}
.bottom{position:fixed;left:0;right:0;bottom:0;background:#fff;border-top:1px solid var(--line);display:flex;justify-content:space-around;padding:6px 0 calc(6px + env(safe-area-inset-bottom));z-index:20}
.bottom button{background:none;border:0;display:flex;flex-direction:column;align-items:center;gap:2px;color:var(--muted);font:600 12px Inter;min-width:64px;min-height:48px;cursor:pointer}
.bottom button.on{color:var(--accent)}
@media(min-width:1024px){.shell{grid-template-columns:280px 1fr}.side{display:flex;flex-direction:column;gap:6px;padding:24px 16px;border-right:1px solid var(--line);background:#fff;position:sticky;top:0;height:100vh}
.bottom{display:none}.main{padding-bottom:40px}}
.side button{display:flex;align-items:center;gap:12px;border:0;background:none;padding:12px 14px;border-radius:14px;font:600 15px Inter;color:var(--muted);cursor:pointer;text-align:left;min-height:44px}
.side button.on{background:#E9EDFC;color:var(--accent)}
.hero-card{background:var(--accent);color:#fff;border:0;display:flex;gap:16px;align-items:center;cursor:pointer;width:100%;text-align:left;font:inherit}
.hero-card h3{color:#fff}.hero-card p{opacity:.85;font-size:14px}
.prog{height:10px;border-radius:99px;background:#E3E6EE;overflow:hidden;margin-top:12px}.prog i{display:block;height:100%;background:var(--ok);border-radius:99px;transition:width .4s}
.stack{display:grid;gap:14px}
.subj{display:flex;gap:14px;align-items:center;cursor:pointer;text-align:left;width:100%;font:inherit;color:inherit}
/* chat */
.chat{display:flex;flex-direction:column;height:calc(100dvh - 40px);max-height:100dvh}
@media(max-width:1023px){.chat{height:calc(100dvh - 96px)}}
.chat-head{display:flex;align-items:center;gap:12px;padding-bottom:12px;border-bottom:1px solid var(--line)}
.chat-head .grow{flex:1}.chat-head small{color:var(--muted)}
.msgs{flex:1;overflow-y:auto;padding:16px 0;display:flex;flex-direction:column;gap:12px}
.msg{max-width:88%;padding:12px 16px;border-radius:18px;word-wrap:break-word;overflow-wrap:anywhere}
.msg.user{align-self:flex-end;background:var(--accent);color:#fff;border-bottom-right-radius:6px}
.msg.assistant{align-self:flex-start;background:#fff;border:1px solid var(--line);border-bottom-left-radius:6px}
.msg img{max-width:100%;border-radius:12px;display:block;margin-bottom:8px}
.msg .tools{display:flex;gap:8px;flex-wrap:wrap;margin-top:10px}
.tool{min-height:36px;padding:0 14px;border-radius:999px;border:1px solid var(--line);background:#fff;font:600 13px Inter;color:var(--muted);cursor:pointer}
.tool.sel{background:#E3F5EE;color:var(--ok);border-color:#BFE6D8}.tool.sel.neg{background:var(--warn-bg);color:var(--warn);border-color:#F2D6A8}
.trans{margin-top:10px;padding-top:10px;border-top:1px dashed var(--line);font-size:15px;color:var(--muted)}
.composer{display:flex;gap:8px;align-items:flex-end;padding-top:10px;border-top:1px solid var(--line);position:relative}
.composer textarea{min-height:46px;max-height:140px;resize:none;border-radius:23px}
.round{width:46px;height:46px;min-width:46px;border-radius:50%;border:1px solid var(--line);background:#fff;display:grid;place-items:center;cursor:pointer;color:var(--text)}
.round.send{background:var(--accent);border-color:var(--accent);color:#fff}
.preview{display:flex;gap:10px;align-items:center;padding:8px 0}.preview img{height:56px;border-radius:10px}
.drop{position:absolute;inset:0;background:rgba(47,75,216,.92);color:#fff;display:none;place-items:center;font:700 22px Manrope;z-index:30}
.drop.show{display:grid}
.menu-pop{position:absolute;bottom:58px;left:0;background:#fff;border:1px solid var(--line);border-radius:16px;padding:6px;display:none;z-index:5;box-shadow:0 8px 24px rgba(20,22,27,.1)}
.menu-pop.show{display:block}.menu-pop button{display:flex;gap:10px;align-items:center;border:0;background:none;padding:10px 14px;font:600 14px Inter;cursor:pointer;width:100%;min-height:44px;border-radius:10px}
.dots span{display:inline-block;width:7px;height:7px;border-radius:50%;background:var(--muted);margin:0 2px;animation:b 1s infinite}.dots span:nth-child(2){animation-delay:.15s}.dots span:nth-child(3){animation-delay:.3s}
@keyframes b{50%{opacity:.25}}
.modal{position:fixed;inset:0;background:rgba(20,22,27,.5);display:grid;place-items:center;padding:20px;z-index:50}
.modal .card{max-width:420px}
.hidden{display:none!important}