:root{color:#102654;background:#fbf8f7;font-family:Outfit,PingFang SC,Microsoft YaHei,sans-serif;font-synthesis:none;text-rendering:optimizeLegibility;--ink: #102654;--muted: #657087;--line: #d9dce4;--surface: #ffffff;--surface-soft: rgba(255, 255, 255, .86);--shadow: 0 18px 44px rgba(47, 38, 61, .09);--shadow-small: 0 8px 22px rgba(47, 38, 61, .08);--radius-xl: 28px;--radius-lg: 20px;--radius-md: 14px;--accent: #7856d8;--accent-dark: #5e3fc4;--accent-soft: #f0ebff;--accent-border: #b9a5f2;--operand-one: #5c91ec;--operand-two: #f3b64e;--carry: #e8689a;--answer: #4ab18b}*{box-sizing:border-box}html{min-width:320px;background:#fbf8f7}body{min-width:320px;min-height:100vh;min-height:100dvh;margin:0;overflow-x:hidden;background:radial-gradient(circle at 83% 10%,rgba(251,218,229,.46),transparent 30%),radial-gradient(circle at 18% 88%,rgba(221,213,250,.5),transparent 31%),radial-gradient(circle at 70% 90%,rgba(208,242,225,.42),transparent 28%),#fbf8f7}button{color:inherit;font:inherit;touch-action:manipulation;-webkit-tap-highlight-color:transparent}button:focus-visible,[tabindex]:focus-visible{outline:3px solid color-mix(in srgb,var(--accent) 75%,white);outline-offset:3px}button:disabled{cursor:not-allowed;opacity:.42}[data-operation=addition]{--accent: #477fdc;--accent-dark: #2f66bd;--accent-soft: #eaf2ff;--accent-border: #9ab9ed}[data-operation=subtraction]{--accent: #ed7649;--accent-dark: #d75a2f;--accent-soft: #fff0e9;--accent-border: #f1aa8e}[data-operation=multiplication]{--accent: #7856d8;--accent-dark: #5e3fc4;--accent-soft: #f0ebff;--accent-border: #b9a5f2}[data-operation=division]{--accent: #30a977;--accent-dark: #17865b;--accent-soft: #e9f8f1;--accent-border: #8bd3b5}.app-brand{display:flex;align-items:center;justify-content:center;gap:16px;min-width:0}.app-brand img{width:68px;height:68px;flex:0 0 auto;filter:drop-shadow(0 7px 12px rgba(61,45,67,.12))}.app-brand p{margin:0}.app-brand__title{color:var(--ink);font-family:ZCOOL KuaiLe,Outfit,sans-serif;font-size:clamp(2.45rem,4vw,3.7rem);font-weight:400;line-height:1;letter-spacing:.015em}.app-brand__subtitle{margin-top:8px!important;color:#50586c;font-size:clamp(1rem,1.6vw,1.25rem);font-weight:700;letter-spacing:.05em}.app-brand--compact{justify-content:flex-start;gap:10px}.app-brand--compact img{width:44px;height:44px}.app-brand--compact .app-brand__title{white-space:nowrap;font-size:clamp(1.5rem,2.3vw,2rem)}.operation-picker{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));width:min(100%,1000px);min-height:64px;overflow:hidden;border:1px solid rgba(119,119,136,.22);border-radius:18px;background:#ffffffd4;box-shadow:0 8px 22px #372b420a;-webkit-backdrop-filter:blur(16px);backdrop-filter:blur(16px)}.operation-picker__button{position:relative;min-width:0;min-height:58px;border:0;border-right:1px solid rgba(119,119,136,.15);background:transparent;cursor:pointer;font-size:1.08rem;font-weight:800;transition:background-color .16s ease,color .16s ease,box-shadow .16s ease}.operation-picker__button:last-child{border-right:0}.operation-picker__button span{display:inline-block;margin-right:12px;color:var(--button-accent);font-size:1.9rem;font-weight:800;line-height:1;vertical-align:-.08em}.operation-picker__button[data-operation=addition]{--button-accent: #477fdc}.operation-picker__button[data-operation=subtraction]{--button-accent: #f07143}.operation-picker__button[data-operation=multiplication]{--button-accent: #7856d8}.operation-picker__button[data-operation=division]{--button-accent: #30a977}.operation-picker__button:hover{background:#f7f7fbe6}.operation-picker__button[aria-pressed=true]{z-index:1;color:var(--button-accent);background:color-mix(in srgb,var(--button-accent) 8%,white);box-shadow:inset 0 0 0 2px color-mix(in srgb,var(--button-accent) 58%,white);border-radius:17px}.operation-picker--compact{width:min(68vw,860px);min-height:52px;border-radius:16px}.operation-picker--compact .operation-picker__button{min-height:50px;font-size:.98rem}.operation-picker--compact .operation-picker__button span{margin-right:8px;font-size:1.5rem}.input-screen{display:flex;flex-direction:column;width:min(100%,1420px);min-height:100vh;min-height:100dvh;margin:0 auto;padding:max(18px,env(safe-area-inset-top)) max(24px,env(safe-area-inset-right)) max(12px,env(safe-area-inset-bottom)) max(24px,env(safe-area-inset-left))}.input-screen__header{display:flex;flex-direction:column;align-items:center;gap:16px;flex:0 0 auto}.input-screen__content{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1fr);gap:24px;width:min(100%,1240px);margin:20px auto 0}.input-card,.problem-library{min-width:0;border:1px solid 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16px;color:var(--ink);font-size:1.26rem;font-weight:800;letter-spacing:.03em}.difficulty-grid,.example-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px}.library-option,.example-option{min-width:0;min-height:64px;border:1px solid #dcdce2;border-radius:14px;background:#fff;cursor:pointer;font-weight:800;transition:border-color .15s ease,box-shadow .15s ease,transform .1s ease}.library-option:hover,.example-option:hover{border-color:var(--accent);box-shadow:var(--shadow-small)}.library-option:active,.example-option:active{transform:translateY(1px)}.library-option[aria-pressed=true]{border-color:var(--accent);box-shadow:inset 0 0 0 1px var(--accent),0 8px 18px color-mix(in srgb,var(--accent) 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max(14px,env(safe-area-inset-bottom)) max(5vw,env(safe-area-inset-left))}.lesson-screen__toolbar{display:flex;align-items:center;justify-content:space-between;gap:22px}.lesson-heading{display:grid;grid-template-columns:1fr minmax(180px,.45fr);align-items:center;gap:24px;min-width:0}.lesson-heading>div:first-child{display:flex;align-items:baseline;gap:16px;min-width:0}.lesson-heading h1{overflow:hidden;margin:0;color:var(--ink);font-size:clamp(2rem,4.2vw,4.4rem);font-weight:800;line-height:1;letter-spacing:.02em;text-overflow:ellipsis;white-space:nowrap}.lesson-heading h1:focus-visible{outline:none}.lesson-heading p{flex:0 0 auto;margin:0;color:var(--muted);font-size:1rem;font-weight:700}.lesson-progress{height:10px;overflow:hidden;border-radius:999px;background:#e5e3e9}.lesson-progress i{display:block;height:100%;border-radius:inherit;background:linear-gradient(90deg,var(--accent),color-mix(in srgb,var(--accent) 58%,white));transition:width .25s 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65%,white);color:var(--accent-dark);background:color-mix(in srgb,var(--accent-soft) 72%,white)}.lesson-workspace{display:grid;grid-template-columns:minmax(0,1.1fr) minmax(340px,.9fr);gap:20px;min-height:0}.board-panel,.explanation-panel{min-width:0;min-height:0;border:1px solid rgba(119,113,126,.14);border-radius:var(--radius-xl);background:#ffffffe8;box-shadow:var(--shadow)}.board-panel{display:grid;overflow:hidden;place-items:center;padding:clamp(14px,2.2vw,28px)}.explanation-panel{display:flex;flex-direction:column;justify-content:center;padding:clamp(22px,3vw,38px);background:linear-gradient(135deg,color-mix(in srgb,var(--accent-soft) 50%,white),#fff 58%),#fff}.explanation-panel__meta{display:flex;align-items:center;gap:14px;min-width:0}.explanation-panel__meta span{flex:0 0 auto;padding:7px 11px;border-radius:9px;color:#fff;background:var(--accent);font-size:.82rem;font-weight:800}.explanation-panel__meta strong{overflow:hidden;font-size:1.25rem;text-overflow:ellipsis;white-space:nowrap}.explanation-panel__live h2{margin:22px 0 10px;color:var(--ink);font-size:clamp(1.55rem,2.4vw,2.15rem);line-height:1.18}.explanation-panel__live p{margin:0;color:#303b57;font-size:clamp(1rem,1.45vw,1.22rem);font-weight:700;line-height:1.6}.lesson-legend{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px 18px;margin-top:24px;padding-top:18px;border-top:1px dashed #d5d3da}.lesson-legend__item{display:flex;align-items:center;min-width:0;color:#475069;font-size:.83rem;font-weight:700}.lesson-legend__item i{width:17px;height:17px;margin-right:8px;border:2px solid var(--legend-color);border-radius:5px;background:color-mix(in srgb,var(--legend-color) 14%,white)}.lesson-legend__item--1{--legend-color: var(--operand-one)}.lesson-legend__item--2{--legend-color: var(--operand-two)}.lesson-legend__item--3{--legend-color: var(--carry)}.lesson-legend__item--4{--legend-color: var(--answer)}.playback-controls{display:grid;grid-template-columns:repeat(7,minmax(0,1fr));gap:9px;padding:10px 12px;border:1px solid rgba(119,113,126,.15);border-radius:18px;background:#ffffffe8;box-shadow:var(--shadow);-webkit-backdrop-filter:blur(16px);backdrop-filter:blur(16px)}.playback-controls button{min-width:0;min-height:48px;padding:8px;border:1px solid #dcdae1;border-radius:13px;background:#fff;cursor:pointer;font-size:.89rem;font-weight:800;white-space:nowrap}.playback-controls button:hover:not(:disabled){border-color:var(--accent-border);background:var(--accent-soft)}.playback-controls .playback-controls__primary{border-color:var(--accent);color:#fff;background:linear-gradient(135deg,var(--accent),var(--accent-dark));box-shadow:0 8px 18px color-mix(in srgb,var(--accent) 22%,transparent)}.playback-controls 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.is-target{color:var(--accent-dark);font-weight:800}.column-board__carry,.multiplication-board__carry{min-height:25px}.column-board__row-label,.multiplication-board__row-label{color:#94939b;font-size:.57rem;font-weight:700;text-align:center}.column-board__carry-chip,.multiplication-board__carry-chip{display:grid;width:24px;height:24px;margin:auto;place-items:center;border-radius:50%;color:var(--carry);opacity:0;font-size:1rem;font-weight:800}.column-board__carry-chip.is-visible,.multiplication-board__carry-chip.is-visible{opacity:1}.column-board__carry-chip.is-used,.multiplication-board__carry-chip.is-used{color:#bd567f}.column-board__carry-chip.is-focused,.multiplication-board__carry-chip.is-focused{box-shadow:0 0 0 3px color-mix(in srgb,var(--carry) 28%,transparent);animation:ink-pulse .7s ease-out}.column-board__row,.multiplication-board__row,.subtraction-board__row{min-height:58px}.column-board__sign,.multiplication-board__sign,.subtraction-board__sign{color:#1a204b;font-size:2.45rem;font-weight:800;text-align:center}.column-board__digit,.multiplication-board__digit,.subtraction-board__digit,.subtraction-board__answer{display:grid;min-width:0;min-height:50px;place-items:center;border:2px solid transparent;border-radius:13px;color:#131941;font-size:clamp(2.2rem,4.3vw,3.8rem);font-weight:800;line-height:1;opacity:0}.column-board__digit.is-visible,.multiplication-board__digit.is-visible,.subtraction-board__digit,.subtraction-board__answer.is-visible{opacity:1}.column-board__digit.is-focused,.multiplication-board__digit.is-focused,.subtraction-board__digit.is-focused,.subtraction-board__answer.is-focused{border-color:var(--accent);background:color-mix(in srgb,var(--accent-soft) 62%,white);animation:ink-pulse .6s ease-out}.column-board__digit.is-context,.multiplication-board__digit.is-context{opacity:1;background:color-mix(in srgb,var(--accent-soft) 30%,white)}.column-board__row--top .column-board__digit,.multiplication-board__row--top .multiplication-board__digit{color:#2f6fc7}.column-board__row--bottom .column-board__digit,.multiplication-board__row--mult .multiplication-board__digit{color:#df783f}.column-board__row--ans .column-board__digit,.multiplication-board__row--ans .multiplication-board__digit,.subtraction-board__answer{color:#248763}.column-board__rule,.multiplication-board__rule,.subtraction-board__rule{height:4px;margin:5px 3% 7px calc(2.8rem + 3%);border-radius:999px;background:#171d47}.column-board__bubble,.multiplication-board__bubble{position:absolute;top:34px;right:0;display:flex;flex-direction:column;align-items:center;padding:7px 10px;border:1px solid #eed06a;border-radius:12px;background:#fff8cc;box-shadow:var(--shadow-small)}.column-board__bubble span,.multiplication-board__bubble small{color:#746530;font-size:.65rem}.column-board__bubble strong,.multiplication-board__bubble strong{font-size:1.3rem}.column-board--addition .column-board__bubble{top:0}.column-board--addition .column-board__carry-chip{position:relative;z-index:2;top:118px;justify-self:end;margin:0 8px 0 0}.multiplication-board{padding-top:64px}.multiplication-board__bubble{top:0;white-space:nowrap}.multiplication-board__carry-chip{justify-self:end;margin:0 .5rem 0 0}.multiplication-board__carry-chip.is-used{color:#171d47}.multiplication-board.is-two-layer .multiplication-board__row{min-height:46px}.multiplication-board.is-two-layer .multiplication-board__digit{min-height:42px;font-size:clamp(1.85rem,3.3vw,2.95rem)}.multiplication-board__sign{display:grid;min-width:0;place-items:center}.multiplication-board__sign small{color:#757685;font-size:.52rem;font-weight:800;line-height:1.1}.multiplication-board__digit.is-resting{opacity:.28}.multiplication-board__digit.is-placeholder{color:#aaa8b5;font-size:.82em}.multiplication-board__rule--answer{opacity:0}.multiplication-board__rule--answer.is-visible{opacity:1}.multiplication-board__temp{position:absolute;right:0;bottom:4px;padding:6px 10px;border-radius:10px;color:#6a5621;background:#fff4ba;font-size:.7rem;font-weight:800}.subtraction-board__borrow-layer{position:relative;height:28px}.subtraction-board__sign{justify-self:center;transform:translate(clamp(2.85rem,4.1vw,3.3rem))}.subtraction-board__digit{position:relative}.subtraction-board__digit.is-changed{overflow:visible}.subtraction-board__original{position:relative;z-index:1}.subtraction-board__borrow-dot{position:absolute;z-index:3;top:-8px;left:50%;width:8px;height:8px;border-radius:50%;background:var(--carry);box-shadow:0 0 0 3px color-mix(in srgb,var(--carry) 14%,transparent);transform:translate(-50%)}.subtraction-board__borrow-dot.is-history{width:8px;height:8px;background:#171d47;box-shadow:none;opacity:1}.subtraction-board__rewrite{position:absolute;z-index:2;top:50%;display:flex;align-items:center;gap:2px;color:var(--carry);font-size:1rem;font-weight:900;line-height:1;pointer-events:none;transform:translateY(-50%);white-space:nowrap}.subtraction-board__rewrite.is-source{left:calc(50% + 1rem)}.subtraction-board__rewrite.is-receiver{right:calc(50% + 1rem)}.subtraction-board__rewrite-before,.subtraction-board__rewrite-after{font:inherit;line-height:1}.subtraction-board__rewrite-before{color:#767681;font-size:.68rem}.subtraction-board__rewrite-after{font-size:.84rem;text-shadow:0 1px 0 white}.subtraction-board__rewrite-arrow{flex:0 0 auto;width:22px;height:10px;overflow:visible;fill:none;stroke:currentColor;stroke-linecap:round;stroke-linejoin:round;stroke-width:2.15}.subtraction-board__rewrite.is-history{color:#888791;opacity:.24}.subtraction-board__rewrite.is-history.is-source{left:calc(50% + 1.1rem)}.subtraction-board__rewrite.is-history.is-receiver{right:calc(50% + 1.1rem)}.subtraction-board__rewrite.is-history .subtraction-board__rewrite-after{text-shadow:none}@media(max-width:640px){.subtraction-board[data-columns="3"] .subtraction-board__sign{font-size:1.75rem;transform:translate(2.75rem)}.subtraction-board[data-columns="3"] .subtraction-board__rewrite.is-current.is-source{right:4px;left:auto;gap:0}.subtraction-board[data-columns="3"] .subtraction-board__rewrite.is-current.is-receiver{right:calc(50% + .64rem);left:auto;gap:0}.subtraction-board[data-columns="3"] .subtraction-board__rewrite-before{font-size:.58rem}.subtraction-board[data-columns="3"] .subtraction-board__rewrite-after{font-size:.72rem}.subtraction-board[data-columns="3"] .subtraction-board__rewrite-arrow{width:14px;height:12px}}@media(max-width:360px){.subtraction-board[data-columns="3"] .subtraction-board__rewrite.is-current.is-source{right:-2px}.subtraction-board[data-columns="3"] .subtraction-board__rewrite.is-current.is-receiver{right:calc(50% + .8rem)}.subtraction-board[data-columns="3"] .subtraction-board__rewrite-before{font-size:.5rem}.subtraction-board[data-columns="3"] .subtraction-board__rewrite-after{font-size:.66rem}.subtraction-board[data-columns="3"] .subtraction-board__rewrite-arrow{width:8px}}.subtraction-board__row--answer{min-height:68px}.division-board{display:grid;grid-template-columns:minmax(0,1fr) 84px;align-items:center;gap:12px;width:min(100%,680px)}.division-board__paper{min-width:0;overflow:auto;padding:20px 10px}.division-board__frame{display:grid;grid-template-columns:max-content minmax(210px,1fr);align-items:center;min-width:290px}.division-board__digit-row{display:grid;min-height:45px}.division-board__digit{display:grid;min-width:0;place-items:center;border-radius:10px;font-size:clamp(1.75rem,3.6vw,3rem);font-weight:800}.division-board__digit.is-current{color:#2e5fb8;background:#edf3ff}.division-board__digit.is-product{color:#dc684f;background:#fff0eb}.division-board__digit.is-remainder{color:#248763;background:#e9f8f1}.division-board__digit.is-quotient{color:#6446c4;background:#f0ebff}.division-board__divisor{align-self:stretch;display:flex;align-items:center;justify-content:flex-end;padding:0 10px 0 0;font-size:clamp(1.8rem,3.8vw,3.1rem);font-weight:800}.division-board__digit-row--dividend{position:relative;border-top:3px solid transparent}.division-board__digit-row--dividend:before{position:absolute;inset:-3px 0 0 -6px;border-top:3px solid #17204b;border-left:3px solid #17204b;border-radius:13px 0 0;content:"";pointer-events:none}.division-board__minus{padding-right:9px;font-size:2rem;font-weight:800;text-align:right}.division-board__rule{height:3px;margin:2px 2%;border-radius:999px;background:#35385c}.division-board__round-guide{display:grid;gap:8px}.division-board__round-guide span{display:flex;align-items:center;justify-content:space-between;min-height:42px;padding:7px 9px;border-radius:10px;color:#6d7080;background:#f7f7fa;font-size:.67rem;font-weight:700}.division-board__round-guide strong{color:var(--ink);font-size:1rem}@keyframes ink-pulse{0%{transform:scale(.92)}60%{transform:scale(1.04)}to{transform:scale(1)}}@media(max-width:980px){.input-screen__content{grid-template-columns:minmax(0,1fr);width:min(100%,680px)}.problem-library{min-height:420px}.lesson-screen{display:block;padding-right:max(18px,env(safe-area-inset-right));padding-left:max(18px,env(safe-area-inset-left))}.lesson-screen>*+*{margin-top:12px}.lesson-screen__toolbar{align-items:stretch;flex-direction:column}.operation-picker--compact{width:100%}.lesson-workspace{grid-template-columns:minmax(0,1fr)}.board-panel{min-height:420px}.explanation-panel{min-height:280px}.playback-controls{position:sticky;z-index:5;bottom:max(8px,env(safe-area-inset-bottom));grid-template-columns:repeat(4,minmax(0,1fr))}}@media(max-width:640px){.input-screen{padding-right:max(12px,env(safe-area-inset-right));padding-left:max(12px,env(safe-area-inset-left))}.input-screen__header{gap:14px}.app-brand{gap:10px}.app-brand img{width:52px;height:52px}.app-brand__title{font-size:clamp(1.85rem,9vw,2.55rem)}.app-brand__subtitle{margin-top:4px!important;font-size:.78rem}.operation-picker{grid-template-columns:repeat(2,minmax(0,1fr));border-radius:18px}.operation-picker__button{min-height:52px;border-bottom:1px solid rgba(119,119,136,.15);font-size:.92rem}.operation-picker__button:nth-child(2n){border-right:0}.operation-picker__button:nth-last-child(-n+2){border-bottom:0}.operation-picker--compact{grid-template-columns:repeat(4,minmax(0,1fr));min-height:48px}.operation-picker--compact .operation-picker__button{min-height:46px;border-right:1px solid rgba(119,119,136,.15);border-bottom:0;font-size:.74rem}.operation-picker--compact .operation-picker__button:last-child{border-right:0}.operation-picker--compact .operation-picker__button span{margin-right:4px;font-size:1rem}.operation-picker__button span{margin-right:8px;font-size:1.45rem}.input-screen__content{gap:14px;margin-top:14px}.input-card,.problem-library{border-radius:22px}.input-card{padding:18px 14px}.operand-line{gap:7px}.operand-box{min-height:88px;border-radius:15px}.operand-box>span{font-size:clamp(2.2rem,13vw,3.4rem)}.operand-box>small{overflow:hidden;max-width:100%;font-size:.62rem;text-overflow:ellipsis;white-space:nowrap}.operand-line__symbol{flex-basis:30px;font-size:2.5rem}.number-pad{gap:9px}.number-pad button{min-height:54px;font-size:1.55rem}.primary-action{min-height:56px}.problem-library{min-height:0;padding:22px 16px}.difficulty-grid,.example-grid{gap:9px}.library-option{min-height:60px;padding:7px;font-size:.78rem}.example-option{min-height:78px}.lesson-screen{padding-top:max(10px,env(safe-area-inset-top))}.lesson-screen__toolbar{gap:9px}.lesson-heading{grid-template-columns:minmax(0,1fr);gap:9px}.lesson-heading h1{font-size:2.25rem}.stage-rail button{flex-basis:128px;min-height:50px;font-size:.78rem}.board-panel{min-height:330px;padding:14px 8px}.explanation-panel{min-height:260px;padding:22px 18px}.lesson-legend{gap:9px}.playback-controls{grid-template-columns:repeat(4,minmax(0,1fr));gap:7px;padding:8px}.playback-controls button{min-height:46px;padding:6px 4px;font-size:.72rem}.column-board__digit,.multiplication-board__digit,.subtraction-board__digit,.subtraction-board__answer{font-size:clamp(1.8rem,10vw,3rem)}.division-board{grid-template-columns:minmax(0,1fr)}.division-board__round-guide{grid-template-columns:repeat(4,minmax(0,1fr))}.division-board__round-guide span{flex-direction:column}}@media(min-width:981px)and (max-height:800px){.input-screen{padding-top:10px}.input-screen__header{gap:10px}.app-brand img{width:52px;height:52px}.app-brand__title{font-size:2.35rem}.app-brand__subtitle{margin-top:3px!important;font-size:.9rem}.operation-picker{min-height:52px}.operation-picker__button{min-height:50px}.input-screen__content{margin-top:12px}.input-card{padding-top:18px;padding-bottom:18px}.operand-box{min-height:82px}.number-pad button{min-height:48px}.input-hint{margin-top:6px;margin-bottom:6px}.input-error{margin-top:4px}.primary-action{min-height:50px}.problem-library{gap:13px;padding:20px 26px}.problem-library section+section{padding-top:12px}.library-option{min-height:50px}.example-option{min-height:67px}.lesson-screen{gap:7px;padding-top:8px;padding-bottom:8px}.app-brand--compact img{width:38px;height:38px}.operation-picker--compact,.operation-picker--compact .operation-picker__button{min-height:42px}.lesson-heading h1{font-size:2.65rem}.stage-rail button{min-height:45px}.board-panel,.explanation-panel{border-radius:22px}.playback-controls{padding:7px 9px}.playback-controls button{min-height:42px}}@media(orientation:landscape)and (max-height:480px){.input-screen{min-height:auto}.input-screen__header{align-items:stretch;flex-direction:row}.input-screen__header .operation-picker{flex:1 1 auto}.input-screen__content{grid-template-columns:minmax(0,1fr) minmax(0,1fr);width:100%}.lesson-screen{min-height:auto}.lesson-screen__toolbar{align-items:center;flex-direction:row}.lesson-screen__toolbar .operation-picker{flex:1 1 auto;width:auto;min-width:0}.lesson-workspace{grid-template-columns:minmax(0,1.1fr) minmax(280px,.9fr)}.board-panel,.explanation-panel{min-height:330px}.playback-controls{position:static}}@media(prefers-reduced-motion:reduce){*,*:before,*:after{scroll-behavior:auto!important;animation-duration:.001ms!important;animation-iteration-count:1!important;transition-duration:.001ms!important}}