:root{--bg:#f6f7f9;--card:#fff;--ink:#1b2430;--mute:#5b6675;--line:#e2e6ec;--accent:#1d4ed8;--ok:#15803d;--okbg:#e7f6ec;--bad:#b91c1c;--badbg:#fdeaea}
@media (prefers-color-scheme:dark){:root{--bg:#10141a;--card:#181d25;--ink:#e8ecf2;--mute:#9aa5b5;--line:#2a323d;--accent:#7aa2ff;--ok:#4ade80;--okbg:#12301f;--bad:#f87171;--badbg:#341616}}
*{box-sizing:border-box}
body{margin:0;background:var(--bg);color:var(--ink);font:16px/1.5 system-ui,-apple-system,Segoe UI,Roboto,sans-serif}
#wm{position:fixed;inset:0;pointer-events:none;z-index:50;opacity:.09}
.top{display:flex;justify-content:space-between;align-items:center;padding:12px 16px;background:var(--card);border-bottom:1px solid var(--line);position:sticky;top:0;z-index:10}
#brand{color:var(--ink);text-decoration:none;font-weight:600}
#nav{display:flex;gap:12px;font-size:14px;white-space:nowrap}#brand{font-size:15px}
#nav a,.link{color:var(--accent);cursor:pointer;background:none;border:0;font:inherit;padding:0;text-decoration:none}
main{max-width:720px;margin:0 auto;padding:16px}
h1{font-size:22px;margin:8px 0 4px}h2{font-size:18px;margin:0}
.mute{color:var(--mute)}.small{font-size:13px}
.card{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:16px;margin:12px 0}
input[type=text]{width:100%;padding:14px;font-size:18px;letter-spacing:1px;border:1px solid var(--line);border-radius:10px;background:var(--bg);color:var(--ink);text-transform:uppercase}
.btn{display:inline-block;width:100%;padding:14px;border:0;border-radius:10px;background:var(--accent);color:#fff;font-size:16px;font-weight:600;cursor:pointer;margin-top:12px}
.btn.alt{background:transparent;color:var(--accent);border:1px solid var(--line)}
.btn:disabled{opacity:.5}
.err{color:var(--bad);margin-top:10px}
.set{border-left:6px solid var(--c);padding:0}
.set>summary{list-style:none;cursor:pointer;padding:14px 16px;font-weight:600;display:flex;justify-content:space-between}
.set>summary::after{content:"+";color:var(--mute)}.set[open]>summary::after{content:"–"}
.topic{display:flex;justify-content:space-between;gap:8px;width:100%;text-align:left;background:none;border:0;border-top:1px solid var(--line);padding:12px 16px;font:inherit;color:var(--ink);cursor:pointer}
.topic:hover{background:var(--bg)}
.pill{white-space:nowrap;color:var(--mute);font-size:13px}
.diff{display:grid;grid-template-columns:1fr 1fr;gap:10px}
.diff button{padding:16px;border-radius:10px;border:1px solid var(--line);background:var(--card);color:var(--ink);font:inherit;font-weight:600;cursor:pointer;text-align:left}
.diff button small{display:block;font-weight:400;color:var(--mute)}
.diff button:disabled{opacity:.4;cursor:not-allowed}
.stem{font-size:18px;margin:6px 0 14px}
.choice{display:flex;gap:10px;width:100%;text-align:left;padding:12px 14px;margin:8px 0;border:1px solid var(--line);border-radius:10px;background:var(--card);color:var(--ink);font:inherit;cursor:pointer}
.choice b{min-width:20px}
.choice:not(:disabled):hover{border-color:var(--accent)}
.choice.right{background:var(--okbg);border-color:var(--ok)}
.choice.wrong{background:var(--badbg);border-color:var(--bad)}
.fb{padding:12px 14px;border-radius:10px;margin-top:12px}
.fb.right{background:var(--okbg)}.fb.wrong{background:var(--badbg)}
.bar{height:8px;background:var(--line);border-radius:4px;overflow:hidden;margin-top:6px}.bar i{display:block;height:100%;background:var(--accent)}
table{width:100%;border-collapse:collapse;font-size:14px}td,th{padding:8px 4px;border-top:1px solid var(--line);text-align:left}
details.faq{margin:10px 0}details.faq summary{font-weight:600;cursor:pointer}
.row{display:flex;justify-content:space-between;align-items:center}
.mark{display:inline-grid;place-items:center;width:26px;height:26px;margin-right:8px;border-radius:7px;background:var(--accent);color:#fff;font-weight:800;font-size:17px;vertical-align:middle}
.mark.big{width:64px;height:64px;font-size:40px;border-radius:16px;margin:0}.hero{margin:18px 0 6px}
#brand{display:flex;align-items:center}
.trialbar{position:sticky;top:49px;z-index:9;background:#fef3c7;color:#7c4a03;text-align:center;padding:8px 10px;font-size:13px;font-weight:600}
@media (prefers-color-scheme:dark){.trialbar{background:#3a2e0a;color:#f3d27a}}
.trialbar a{color:inherit;text-decoration:underline}

/* Family / exam / tab picker cards (Home > Family > Exam > Practice-Flashcards-Community) */
.familybtn,.exambtn,.tabbtn{display:flex;flex-direction:column;gap:4px;width:100%;text-align:left;background:var(--card);color:var(--ink);font:inherit;cursor:pointer;border:1px solid var(--line)}
.familybtn:hover,.exambtn:hover,.tabbtn:hover{border-color:var(--accent)}
.familybtn b,.exambtn b,.tabbtn b{font-size:17px}
.card.locked{display:flex;justify-content:space-between;align-items:center;opacity:.6}
.card.locked .pill{background:var(--bg);padding:4px 10px;border-radius:999px}

/* Community chat */
.chatbox{padding:0;display:flex;flex-direction:column;overflow:hidden}
.chatlog{max-height:50vh;overflow-y:auto;padding:14px 16px;display:flex;flex-direction:column;gap:10px}
.msg{max-width:85%;align-self:flex-start}
.msg.mine{align-self:flex-end}
.msgmeta{display:flex;gap:8px;font-size:11px;color:var(--mute);margin-bottom:2px}
.msg.mine .msgmeta{justify-content:flex-end}
.msgbody{background:var(--bg);border-radius:12px;padding:8px 12px;font-size:14px;word-wrap:break-word;white-space:pre-wrap}
.msg.mine .msgbody{background:var(--accent);color:#fff}
.chatform{display:flex;gap:8px;padding:12px 16px;border-top:1px solid var(--line)}
.chatform input{flex:1;padding:10px 12px;font-size:15px;border:1px solid var(--line);border-radius:10px;background:var(--bg);color:var(--ink);text-transform:none;letter-spacing:normal}
.chatform .btn{width:auto;margin-top:0;padding:10px 18px}
.chatbox .err{padding:0 16px 10px}

/* Chess */
.board{display:grid;grid-template-columns:repeat(8,1fr);width:100%;aspect-ratio:1;border:2px solid var(--line);border-radius:8px;overflow:hidden;margin:10px 0}
.sq{border:0;padding:0;font-size:min(7vw,28px);display:flex;align-items:center;justify-content:center;cursor:pointer;line-height:1}
.sq.light{background:#ebecd0}.sq.dark{background:#779556}
@media (prefers-color-scheme:dark){.sq.light{background:#3d4a3a}.sq.dark{background:#25301f}}
.sq.sel{outline:3px solid var(--accent);outline-offset:-3px}
.sq.legal{box-shadow:inset 0 0 0 4px rgba(29,78,216,.55)}
.trivia .stem{font-size:15px}
.trivia .choice{padding:9px 12px;margin:5px 0;font-size:14px}

/* Memory Match */
.memgrid{display:grid;grid-template-columns:repeat(4,1fr);gap:8px;margin:10px 0}
.memtile{aspect-ratio:1;border:1px solid var(--line);border-radius:10px;background:var(--card);color:var(--ink);cursor:pointer;display:flex;align-items:center;justify-content:center;padding:6px}
.memtile .memface{font-size:11px;line-height:1.25;text-align:center;overflow:hidden}
.memtile:not(.flip) .memface{font-size:20px;color:var(--mute)}
.memtile.flip{background:var(--bg);border-color:var(--accent)}
.memtile.matched{background:var(--okbg);border-color:var(--ok);opacity:.7;cursor:default}

/* Word Search */
.wsgrid{display:grid;grid-template-columns:repeat(var(--n),1fr);gap:2px;margin:10px 0;background:var(--line);border:1px solid var(--line);border-radius:8px;overflow:hidden}
.wsq{aspect-ratio:1;border:0;background:var(--card);color:var(--ink);font-size:min(3.6vw,15px);font-weight:600;cursor:pointer;padding:0}
.wsq.sel{background:var(--accent);color:#fff}
.wsq.found{background:var(--okbg);color:var(--ok)}
.wsclue{font-size:13px;padding:4px 0;border-top:1px solid var(--line)}
.wsclue:first-child{border-top:0}
.wsclue.found{color:var(--ok)}

/* Install-to-home-screen modal */
.modalbg{position:fixed;inset:0;background:rgba(0,0,0,.5);display:flex;align-items:center;justify-content:center;z-index:100;padding:16px}
.modal{max-width:360px;width:100%;margin:0}
.modal p{line-height:1.6}

/* Flashcards */
.flashcard{width:100%;min-height:220px;display:flex;flex-direction:column;justify-content:center;gap:10px;text-align:center;cursor:pointer;border:1px solid var(--line);background:var(--card)}
.flashcard.flipped{background:var(--okbg);border-color:var(--ok)}
.flashcard .pill{align-self:center;background:var(--bg);padding:4px 10px;border-radius:999px}
.flashcard .stem{font-size:20px;font-weight:600;margin:8px 0}