*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;font-family:-apple-system,BlinkMacSystemFont,"SF Pro Text","SF Pro Display","Segoe UI",sans-serif;line-height:1.5;-webkit-font-smoothing:antialiased}.wrap{width:min(1100px,calc(100% - 36px));margin:auto}.nav{position:sticky;top:0;z-index:50;backdrop-filter:blur(18px);-webkit-backdrop-filter:blur(18px)}.navin{height:70px;display:flex;align-items:center;justify-content:space-between;gap:18px}.brand{display:flex;align-items:center;gap:10px;text-decoration:none;color:inherit;font-weight:850;font-size:20px}.brand img{width:38px;height:38px;border-radius:10px}.navlinks{display:flex;gap:18px;align-items:center}.navlinks>a:not(.store-badge-link){color:inherit;text-decoration:none;font-weight:650}.badgeimg{height:44px;width:auto;display:block}.footer{padding:38px 0 84px;font-size:14px}.footer .row{display:flex;justify-content:space-between;gap:16px;flex-wrap:wrap}.footer a{color:inherit}.mobilebadge{display:none}.eyebrow{font-size:12px;font-weight:850;letter-spacing:.09em;text-transform:uppercase;padding:7px 10px;border-radius:999px;display:inline-block}.hero h1,.section h2,.article h1{letter-spacing:-.045em;line-height:1.02}.hero h1{font-size:clamp(46px,7vw,78px);margin:18px 0}.hero p{font-size:20px}.section{padding:56px 0}.section h2{font-size:clamp(34px,5vw,52px);margin:0 0 14px}.lead{font-size:19px;max-width:790px}.grid3{display:grid;grid-template-columns:repeat(3,1fr);gap:16px}.card{border-radius:22px;padding:22px}.card h3{margin:4px 0 8px}.actions{display:flex;align-items:center;gap:14px;flex-wrap:wrap;margin-top:26px}.textlink{text-decoration:none;font-weight:800}.article{width:min(800px,calc(100% - 36px));margin:52px auto 90px}.article h1{font-size:clamp(40px,6vw,64px)}.article h2{margin-top:36px}.article p,.article li{font-size:18px}.article .callout{border-radius:20px;padding:20px}.article .back{display:inline-block;margin-bottom:18px;text-decoration:none;font-weight:750}.article .appbox{margin-top:34px;border-radius:24px;padding:24px}.article .appbox h2{margin-top:0}.privacy p{font-size:17px}.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}@media(max-width:820px){.grid3{grid-template-columns:1fr}.navlinks>a:not(.store-badge-link){display:none}.section{padding:42px 0}.mobilebadge{display:block;position:fixed;bottom:max(12px,env(safe-area-inset-bottom));left:50%;transform:translateX(-50%);z-index:80}.mobilebadge img{height:48px;filter:drop-shadow(0 7px 18px rgba(0,0,0,.2))}body{padding-bottom:76px}}
body{background:#f6f8fc;color:#101b31}.nav{background:rgba(246,248,252,.9);border-bottom:1px solid #e1e6ef}.eyebrow{color:#076ce0;background:#e6f2ff}.hero{text-align:center;padding:56px 0 26px}.hero .icon{width:88px;border-radius:22px}.hero p,.lead,.card p,.article p,.article li{color:#657187}.textlink,.article a{color:#176bc3}.game{width:min(780px,calc(100% - 36px));margin:10px auto 56px;background:white;border:1px solid #dfe6ef;border-radius:30px;padding:26px;box-shadow:0 28px 65px rgba(43,70,110,.12)}.gamehead{display:flex;justify-content:space-between;gap:14px;align-items:center}.pill{font-size:12px;font-weight:850;background:#fff0df;color:#d56d00;padding:7px 9px;border-radius:999px}.numbers{display:grid;grid-template-columns:repeat(4,1fr);gap:12px;margin:28px 0}.num{aspect-ratio:1;display:grid;place-items:center;border-radius:22px;background:#e7f2ff;border:1px solid #bedcff;color:#0866cc;font-size:clamp(38px,8vw,58px);font-weight:950;letter-spacing:-.05em}.rule{color:#6c778b;text-align:center}.answerrow{display:grid;grid-template-columns:1fr auto;gap:10px}.answerrow input{min-width:0;border:1px solid #d9e0ea;border-radius:14px;padding:14px;font-size:17px}.button{border:0;border-radius:14px;padding:14px 16px;font-weight:850;cursor:pointer}.orange{background:#ff8a16;color:white}.share{background:#162744;color:white}.feedback{min-height:46px;margin-top:12px;font-weight:800}.feedback.good{color:#11864e}.feedback.bad{color:#bd3c36}.gameactions{display:flex;gap:10px;flex-wrap:wrap}.timer{font-variant-numeric:tabular-nums;color:#6b768a;font-weight:700}.grid3 .card{background:white;border:1px solid #dfe6ef}.cta{text-align:center;background:linear-gradient(135deg,#e9f3ff,#fff2e3);border-radius:30px;padding:36px}.example{font-family:ui-monospace,SFMono-Regular,Menlo,monospace;background:white;border:1px solid #dde5ef;border-radius:16px;padding:16px;white-space:pre-line}.footer{color:#778195}@media(max-width:760px){.answerrow{grid-template-columns:1fr}.hero{padding-top:42px}}
.postsolve{display:flex;align-items:center;justify-content:space-between;gap:14px;background:#eef6ff;border-radius:16px;padding:14px 16px;margin:4px 0 16px}.postsolve[hidden]{display:none}.postsolve strong{color:#154e8c}.postsolve .badgeimg{height:40px}@media(max-width:560px){.postsolve{align-items:flex-start;flex-direction:column}}
@media (prefers-color-scheme: dark){html{color-scheme:dark}}
@media (prefers-color-scheme: dark){body{background:#0b1018;color:#f4f6fa}.nav{background:rgba(11,16,24,.9);border-bottom-color:#29313d}.hero p,.lead,.card p,.article p,.article li{color:#aeb7c6}.eyebrow{color:#82baff;background:#132b48}.game,.grid3 .card{background:#141b25;border-color:#2a3442;box-shadow:none}.num{background:#132b47;border-color:#265382;color:#7dbaff}.rule,.timer,.game-subtitle,.footer{color:#9aa5b5}.answerrow input{background:#0f151e;border-color:#34404f;color:#f4f6fa}.secondary{background:#26303d;color:#e7ebf2}.postsolve{background:#10263f}.postsolve strong{color:#8dc3ff}.cta{background:linear-gradient(135deg,#11253c,#2a1e10)}.example{background:#101721;border-color:#303b49}.textlink,.article a{color:#80baff}}
/* Final polish */
img{max-width:100%;height:auto}a,button{transition:transform .16s ease,opacity .16s ease,box-shadow .16s ease,border-color .16s ease}a:focus-visible,button:focus-visible,input:focus-visible{outline:3px solid currentColor;outline-offset:3px}.store-badge-link:hover{opacity:.88}.navlinks .store-badge-link{flex:none}@media(max-width:820px){.navlinks .store-badge-link{display:none}}@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}a,button{transition:none}}
/* Growth utility + print */
.worksheet{margin:24px 0;border:1px solid #dfe6ef;border-radius:22px;overflow:hidden;background:#fff}.worksheet-head{display:flex;justify-content:space-between;gap:12px;align-items:center;padding:16px 18px;background:#e9f3ff}.worksheet-head span{color:#62728a;font-size:14px}.worksheet-grid{display:grid;grid-template-columns:repeat(2,1fr)}.worksheet-item{min-height:116px;padding:16px;border-top:1px solid #e4e9f0;display:grid;grid-template-columns:auto 1fr;gap:12px;align-content:start}.worksheet-item:nth-child(odd){border-right:1px solid #e4e9f0}.worksheet-item span{font-size:22px;font-weight:850;letter-spacing:.02em}.articletools{display:flex;gap:10px;flex-wrap:wrap;margin:20px 0}.toolbtn{border:1px solid #d6dfeb;background:white;color:#145fae;border-radius:12px;padding:10px 14px;font-weight:800;cursor:pointer}@media(prefers-color-scheme:dark){.worksheet{background:#141b25;border-color:#2a3442}.worksheet-head{background:#13263e}.worksheet-head span{color:#aeb7c6}.worksheet-item{border-top-color:#303a47}.worksheet-item:nth-child(odd){border-right-color:#303a47}.toolbtn{background:#141b25;border-color:#34404f;color:#80baff}}
@media(max-width:620px){.worksheet-grid{grid-template-columns:1fr}.worksheet-item:nth-child(odd){border-right:0}}
@media print{.nav,.footer,.mobilebadge,.back,.eyebrow,.articletools,.appbox{display:none!important}body{background:#fff!important;color:#111!important;padding:0!important}.article{width:100%!important;max-width:none!important;margin:0!important}.article>*{display:none!important}.article>.worksheet,.article>.worksheet+ .articletools{display:block!important}.article>.worksheet+ .articletools{display:none!important}.worksheet{border:0!important;margin:0!important;background:#fff!important}.worksheet-head{display:flex!important;background:#fff!important;border-bottom:2px solid #111!important;padding:0 0 12pt!important}.worksheet-head span{color:#222!important}.worksheet-grid{display:grid!important;grid-template-columns:repeat(2,1fr)!important}.worksheet-item{display:grid!important;min-height:92pt!important;border-color:#bbb!important;break-inside:avoid!important;color:#111!important}.worksheet-item:nth-child(odd){border-right:1px solid #bbb!important}}
.store-badge-link{display:inline-block}.hero-actions{justify-content:center}.secondary{background:#edf1f7;color:#24344f}.game-subtitle{color:#737e90;font-size:14px;margin-top:2px}.article .appbox{background:#e9f3ff}.button:hover,.toolbtn:hover{transform:translateY(-1px)}@media(prefers-color-scheme:dark){.secondary{background:#26303d;color:#e7ebf2}.game-subtitle{color:#9aa5b5}.article .appbox{background:#13263e}}
/* Tap-based practice: mirrors Make24's number → operation → number interaction. */
.practice-help{margin:14px 0 4px;text-align:center;color:#6c778b}.playnumbers{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px;margin:22px 0 12px}.playnum{min-height:78px;border-radius:18px;border:1px solid #bedcff;background:#e7f2ff;color:#0866cc;font-size:34px;font-weight:850;font-family:inherit;cursor:pointer}.playnum.selected{border:2px solid #0874ed;background:#d8ebff;box-shadow:0 0 0 4px rgba(8,116,237,.10)}.playnum:disabled:not(.selected){opacity:.42;cursor:default}.operations{display:grid;grid-template-columns:repeat(4,1fr);gap:10px;margin:12px 0}.opbtn{min-height:54px;border:1px solid #ffd1a3;border-radius:16px;background:#fff0df;color:#d56d00;font-size:25px;font-weight:900;font-family:inherit;cursor:pointer}.opbtn.selected{background:#ff8a16;color:#fff;border-color:#ff8a16;box-shadow:0 0 0 4px rgba(255,138,22,.12)}.opbtn:disabled{opacity:.35;cursor:default}.move-prompt{text-align:center;font-weight:800;min-height:28px;margin:8px 0 18px;color:#41516b}.stepsbox{border:1px solid #e1e7ef;border-radius:18px;padding:14px 16px;background:#f8fafc}.stepshead{display:flex;justify-content:space-between;align-items:center;gap:12px}.steps{margin:10px 0 0;padding-left:22px;min-height:28px;color:#5f6d83}.empty-step{list-style:none;margin-left:-22px;color:#8993a4}.button:disabled{opacity:.42;cursor:default;transform:none!important}@media(max-width:560px){.game{padding:18px}.playnum{min-height:66px;font-size:30px}.opbtn{min-height:50px}.gameactions{display:grid;grid-template-columns:1fr 1fr}.gameactions .button{width:100%}}
@media(prefers-color-scheme:dark){.practice-help{color:#9aa5b5}.playnum{background:#132b47;border-color:#265382;color:#7dbaff}.playnum.selected{background:#17395d;border-color:#5ba6f5;box-shadow:0 0 0 4px rgba(91,166,245,.10)}.opbtn{background:#2b1d0f;border-color:#70461e;color:#ffad59}.opbtn.selected{background:#c86608;border-color:#e77b12;color:#fff}.move-prompt{color:#c3ccd9}.stepsbox{background:#101721;border-color:#303b49}.steps{color:#b1bbc9}.empty-step{color:#7f8b9c}}
.practice-steps{display:grid;grid-template-columns:repeat(3,1fr);gap:8px;margin:16px 0 18px}.practice-steps span{display:flex;align-items:center;justify-content:center;gap:6px;padding:9px 10px;border-radius:13px;background:#f3f6fa;color:#516079;font-size:13px;font-weight:750;text-align:center}.practice-steps b{display:grid;place-items:center;width:22px;height:22px;border-radius:999px;background:#e3efff;color:#0874ed;font-size:12px;flex:none}@media(max-width:560px){.practice-steps{grid-template-columns:1fr}.practice-steps span{justify-content:flex-start}}@media(prefers-color-scheme:dark){.practice-steps span{background:#101721;color:#b8c2d0}.practice-steps b{background:#15375d;color:#75b5ff}}