*{box-sizing:border-box}
html,body{overflow-x:hidden}
body{margin:0;font-family:Rubik,Heebo,Arial,sans-serif;background:#FFF6E8;color:#4A2E1E;-webkit-tap-highlight-color:transparent}
.wrap{max-width:640px;margin:0 auto;padding:18px 16px 30px;position:relative}
.logo{position:absolute;top:12px;left:12px;width:56px;height:56px}
.back{display:inline-block;margin-top:6px;color:#C85A2E;text-decoration:none;font-weight:700;font-size:16px;padding:8px 0}
h1{font-size:28px;margin:22px 0 6px;color:#C85A2E;line-height:1.15;padding-left:64px}
p.sub{margin:0 0 14px;color:#8A6E5E;font-size:16px;line-height:1.45}
.chips{display:flex;gap:8px;overflow-x:auto;padding:4px 2px 10px;scrollbar-width:none}
.chips::-webkit-scrollbar{display:none}
.chip{flex:0 0 auto;border:2px solid #E8D5BF;background:#fff;color:#4A2E1E;border-radius:999px;padding:8px 14px;font:600 15px Rubik,Heebo,Arial,sans-serif;cursor:pointer}
.chip.on{background:#4A2E1E;color:#fff;border-color:#4A2E1E}
.stage{perspective:1400px;margin:6px 0 10px}
.card{position:relative;width:100%;height:470px;cursor:pointer;outline:none}
.inner{position:absolute;inset:0;transform-style:preserve-3d;transition:transform .6s cubic-bezier(.3,1.4,.5,1)}
.inner.spin{transition:transform 1.6s cubic-bezier(.15,.7,.2,1)}
.inner.nt{transition:none}
.face{position:absolute;inset:0;border-radius:26px;backface-visibility:hidden;-webkit-backface-visibility:hidden;overflow:hidden;box-shadow:0 10px 26px rgba(90,58,40,.22);display:flex;flex-direction:column}
.front{background:#fff;border:6px solid var(--c)}
.front .band{background:var(--c);color:#fff;padding:10px 16px;display:flex;justify-content:space-between;align-items:center;font-weight:700;font-size:17px}
.front .num{background:rgba(255,255,255,.25);border-radius:999px;padding:2px 10px;font-size:15px}
.front .body{flex:1;display:flex;flex-direction:column;align-items:center;justify-content:center;text-align:center;padding:14px 20px}
.front .em{font-size:84px;line-height:1;margin-bottom:16px}
.front .q{font-size:25px;font-weight:700;line-height:1.3}
.front .hint{text-align:center;color:#8A6E5E;font-size:15px;padding:0 0 14px}
.face.backf{transform:rotateY(180deg);background:var(--c);color:#fff;padding:18px 18px 16px}
.backf h3{margin:0 0 8px;font-size:19px;display:flex;justify-content:space-between;align-items:center}
.backf ol{margin:0 0 12px;padding-right:1.5em;font-size:17.5px;line-height:1.4}
.backf li{margin-bottom:7px}
.pc{margin-top:auto;background:#fff;color:#4A2E1E;border-radius:18px;padding:12px 14px}
.pc b{display:block;color:var(--c);font-size:17px;margin-bottom:4px}
.pc .st{font-size:17px;font-weight:600;line-height:1.35}
.pc .fr{font-size:14px;color:#8A6E5E;margin-top:6px}
.count{text-align:center;color:#8A6E5E;font-size:15px;margin:2px 0 10px}
.ctrls{display:grid;grid-template-columns:1fr 1fr;gap:10px}
.ctrls button,.big{font:700 19px Rubik,Heebo,Arial,sans-serif;border:0;border-radius:18px;padding:15px 10px;color:#fff;cursor:pointer;box-shadow:0 5px 0 rgba(0,0,0,.14);min-height:56px}
.ctrls button:active,.big:active{transform:translateY(3px);box-shadow:0 2px 0 rgba(0,0,0,.14)}
.rnd{grid-column:1/-1;background:#C85A2E;font-size:22px !important}
.nav{background:#6B4CB0}.shf{background:#2E9C8F}.fsb{background:#E2A12E}
.pdf{display:flex;align-items:center;gap:12px;text-decoration:none;color:#fff;background:#4A2E1E;font-size:20px;font-weight:700;padding:16px 18px;border-radius:18px;margin:16px 0 0;box-shadow:0 6px 0 rgba(0,0,0,.12)}
.pdf small{display:block;font-weight:400;font-size:14px;opacity:.9}
.pdf .e{font-size:28px}
details.teach{background:#fff;border:3px solid #E2A12E;border-radius:20px;margin:18px 0 0;padding:0 16px}
details.teach summary{font-size:20px;font-weight:700;padding:15px 0;cursor:pointer;color:#C85A2E;list-style:none}
details.teach summary::-webkit-details-marker{display:none}
details.teach summary:after{content:" ▾"}
details.teach[open] summary:after{content:" ▴"}
.teach ol{padding-right:20px;line-height:1.55;font-size:16px;margin-top:0}
.teach li{margin-bottom:6px}
.tip{background:#FFF1D6;border-radius:14px;padding:10px 12px;font-size:15.5px;line-height:1.5;margin-bottom:12px}
h2{font-size:21px;color:#6B4CB0;margin:22px 0 10px}
.grid{display:grid;grid-template-columns:repeat(4,1fr);gap:8px}
.tile{background:#fff;border:3px solid var(--c);border-radius:14px;padding:8px 2px;text-align:center;cursor:pointer;font:600 14px Rubik,Heebo,Arial,sans-serif;color:#4A2E1E}
.tile span{display:block;font-size:26px}
.tile.cur{background:var(--c);color:#fff}
footer{text-align:center;color:#8A6E5E;font-size:14px;margin-top:24px}
.xfs{display:none}
@keyframes pop{0%{transform:scale(.92);opacity:.3}100%{transform:scale(1);opacity:1}}
.pop{animation:pop .28s ease-out}
/* full screen for the class board */
body.fs{overflow:hidden;background:#2B1B12}
body.fs .page>*:not(.board){display:none}
body.fs .board{position:fixed;inset:0;z-index:50;background:#2B1B12;display:flex;flex-direction:column;align-items:center;justify-content:center;padding:14px}
body.fs .stage{width:min(96vw,150vh);margin:0 0 12px}
body.fs .card{height:min(76vh,110vw)}
body.fs .chips,body.fs .count{display:none}
body.fs .front .em{font-size:clamp(64px,min(18vh,26vw),190px)}
body.fs .front .q{font-size:clamp(22px,min(6.6vh,7vw),68px)}
body.fs .front .band{font-size:clamp(16px,min(3.4vh,4.6vw),34px)}
body.fs .backf h3{font-size:clamp(18px,min(4.4vh,5vw),42px)}
body.fs .backf ol{font-size:clamp(16px,min(4.8vh,4.8vw),46px)}
body.fs .pc .st{font-size:clamp(16px,min(4.4vh,4.6vw),42px)}
body.fs .pc b{font-size:clamp(15px,min(3.4vh,4.2vw),32px)}
body.fs .pc .fr{font-size:clamp(13px,min(2.6vh,3.6vw),26px)}
body.fs .front .hint{font-size:clamp(13px,min(2.6vh,3.6vw),26px)}
body.fs .ctrls{width:min(96vw,900px);grid-template-columns:repeat(5,1fr)}
body.fs .rnd{grid-column:auto}
body.fs .ctrls button{font-size:17px !important;padding:12px 6px;min-height:50px}
body.fs .xfs{display:block;background:#555}
body.fs .fsb{display:none}
@media (min-width:700px){.card{height:440px}.grid{grid-template-columns:repeat(5,1fr)}}