:root {
  color-scheme:light;
  --ink:#172b43;
  --muted:#53667c;
  --blue:#1765cf;
  --line:#d9e2ed;
  --navy:#0b2038;
  --cyan:#93e8f5;
  --radius:20px;
  font-family:Inter,ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;
  font-size:16px;
  color:var(--ink);
  background:#edf2f8
}
* {
  box-sizing:border-box
}
body {
  margin:0
}
button,input,select {
  font:inherit
}
button,a,input,select {
  -webkit-tap-highlight-color:transparent
}
button,select {
  cursor:pointer
}
button {
  transition:background .18s,transform .18s,box-shadow .18s
}
button:active:not(:disabled) {
  transform:translateY(1px)
}
button:disabled {
  opacity:.38;
  cursor:default
}
button:focus-visible,a:focus-visible,input:focus-visible,select:focus-visible {
  outline:3px solid #eeae35;
  outline-offset:4px
}
button[hidden],[hidden] {
  display:none!important
}
button {
  font-weight:650
}
input,select {
  min-width:0
}
input {
  user-select:text
}
a {
  color:inherit
}
.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
}
.topbar {
  height:76px;
  display:flex;
  align-items:center;
  gap:28px;
  padding:0 max(24px,calc((100vw - 1440px)/2));
  background:#fff;
  border-bottom:1px solid var(--line)
}
.brand {
  display:flex;
  align-items:center;
  gap:11px;
  font-weight:750;
  font-size:18px;
  letter-spacing:-.6px;
  text-decoration:none;
  white-space:nowrap
}
.brand-mark {
  background:#143252;
  color:#bceef6;
  border-radius:9px;
  padding:5px 8px;
  font-family:Georgia,serif;
  font-style:italic;
  font-size:25px;
  letter-spacing:-2px
}
.workspace-label {
  padding-left:28px;
  border-left:1px solid var(--line);
  color:var(--muted);
  font-size:14px
}
.quiet {
  margin-left:auto;
  background:#fff;
  border:1px solid var(--line);
  border-radius:9px;
  padding:10px 16px;
  color:var(--ink)
}
.quiet:hover {
  background:#edf3fa
}
main {
  max-width:1488px;
  padding:28px 24px 18px;
  margin:auto
}
.entry {
  background:#fff;
  border:1px solid var(--line);
  border-radius:var(--radius);
  padding:24px 28px;
  margin-bottom:24px;
  box-shadow:0 3px 8px #17335a04
}
.entry-heading {
  display:flex;
  align-items:baseline;
  justify-content:space-between;
  gap:16px;
  margin-bottom:18px
}
h1 {
  font-size:23px;
  letter-spacing:-.65px;
  font-weight:720;
  margin:0
}
.entry-heading>span {
  font-size:14px;
  color:var(--muted)
}
#equation-form {
  display:flex;
  gap:12px
}
#equation-input {
  flex:1;
  border:1px solid #b6c7dc;
  border-radius:10px;
  padding:14px 18px;
  font-size:24px;
  letter-spacing:.3px;
  background:#f7faff;
  color:var(--ink)
}
.primary {
  border:0;
  background:var(--blue);
  color:white;
  border-radius:10px;
  padding:14px 22px;
  white-space:nowrap;
  box-shadow:0 3px 0 #0c4599
}
.primary:hover {
  background:#1055b6
}
.primary span {
  margin-left:14px
}
.entry-footer {
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:16px;
  margin-top:13px
}
.entry-footer p {
  margin:0;
  font-size:13px;
  color:var(--muted);
  line-height:1.6
}
.entry-footer code {
  font-size:13px
}
.examples {
  display:flex;
  align-items:center;
  gap:8px;
  font-size:13px;
  color:var(--muted);
  white-space:nowrap
}
.examples select {
  font-size:13px;
  max-width:205px;
  background:#fff;
  color:var(--ink);
  border:0;
  border-bottom:1px solid var(--line);
  padding:4px 2px
}
.error {
  font-size:14px;
  line-height:1.5;
  color:#b12736;
  margin:8px 0 0
}
.error:empty {
  display:none
}
.workspace-grid {
  display:grid;
  grid-template-columns:minmax(0,1fr) 310px;
  gap:24px;
  align-items:start
}
.board {
  min-width:0;
  background:var(--navy);
  color:#e8f2ff;
  border:1px solid #284561;
  border-radius:var(--radius);
  box-shadow:0 15px 35px #0a23452b;
  overflow:hidden
}
.board-heading {
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:16px;
  padding:23px 26px;
  border-bottom:1px solid #c0d8ef16
}
.board-heading>div:first-child {
  display:flex;
  align-items:center;
  gap:20px
}
.eyebrow {
  color:#a4b9cd;
  font-size:11px;
  letter-spacing:1.8px;
  font-weight:750
}
#goal {
  font-size:15px;
  font-weight:600
}
.history-controls {
  display:flex;
  gap:8px
}
.history-controls button {
  border:1px solid #536a7f;
  background:#16304b;
  color:#e8f2ff;
  border-radius:8px;
  padding:7px 10px;
  font-size:20px
}
.history-controls span {
  font-size:13px;
  vertical-align:2px
}
.equation-stage {
  position:relative;
  min-height:295px;
  display:flex;
  align-items:center;
  padding:60px 24px 55px;
  background-image:radial-gradient(ellipse at 50% 120%,#1a526569,transparent 70%),radial-gradient(#7592b018 .7px,transparent .7px);
  background-size:auto,22px 22px;
  isolation:isolate
}
.side-caption {
  position:absolute;
  top:24px;
  font-size:10px;
  letter-spacing:2px;
  color:#819bb4;
  font-weight:700
}
.left-caption {
  left:27px
}
.right-caption {
  right:27px
}
.equation {
  display:grid;
  grid-template-columns:minmax(0,1fr) 38px minmax(0,1fr);
  gap:14px;
  width:100%;
  align-items:center
}
.equation-side {
  display:flex;
  flex-wrap:wrap;
  align-items:center;
  justify-content:center;
  gap:10px;
  min-width:0
}
.equals {
  font-family:Georgia,serif;
  font-size:43px;
  text-align:center;
  color:#acc5dd;
  font-weight:400
}
.term {
  touch-action:none;
  user-select:none;
  display:inline-flex;
  align-items:center;
  justify-content:center;
  min-height:72px;
  max-width:100%;
  border:1px solid #7ee4f675;
  border-radius:12px;
  background:linear-gradient(150deg,#235368,#153f57);
  box-shadow:inset 0 1px 0 #c6ffff2b,0 4px 0 #071827,0 7px 12px #0002;
  padding:12px 16px;
  color:var(--cyan);
  font-size:29px;
  font-weight:500;
  position:relative;
  cursor:grab
}
.term:active { cursor:grabbing; }
.dragging-term, .dragging-term * { cursor:grabbing!important; user-select:none; }
.term.drag-source { opacity:.25; }
.term.drag-ghost {
  position:fixed;
  z-index:50;
  pointer-events:none;
  opacity:.95;
  transform:rotate(-3deg) scale(1.06);
  box-shadow:0 18px 35px #0005;
  border-color:#e9cc8e;
}
.term.drag-ghost.valid-drop { border-color:#96efd0; box-shadow:0 0 0 4px #8ae6c044,0 18px 35px #0005; }
.term.combine-candidate { outline:2px dashed #80dcb7; outline-offset:5px; }
.term.combine-target { border-color:#c6ffdf; box-shadow:0 0 0 5px #8ae6c055,0 8px 22px #0004; }
.equation-stage.drag-over-left { box-shadow:inset 48vw 0 80px -60px #4fcea927; }
.equation-stage.drag-over-right { box-shadow:inset -48vw 0 80px -60px #4fcea927; }
.drag-over-left .equation-side[data-side=left], .drag-over-right .equation-side[data-side=right] {
  outline:2px dashed #80dcb7;
  outline-offset:12px;
  border-radius:10px;
}
.cancelling-term:after {
  content:"";
  position:absolute;
  left:5px;
  right:5px;
  top:50%;
  height:3px;
  background:#ffc6a7;
  transform:rotate(-14deg);
  animation:cancel-stroke .3s ease-out;
}
@keyframes cancel-stroke { from { transform:rotate(-14deg) scaleX(0); } to { transform:rotate(-14deg) scaleX(1); } }
.step-proof { opacity:.72; margin-bottom:10px; font-size:16px; }
.selection-bar { flex-wrap:wrap; }
.selection-bar>span { flex:1; min-width:170px; }
#move-selection, #combine-selection { color:#b0f0d8; border:1px solid #6fc8a755; border-radius:6px; padding:7px 9px; }
.equation-stage.distributing { padding:24px; }
.distributing>.equation, .distributing>.side-caption { position:absolute; visibility:hidden; }
.distribution-demo { width:100%; min-width:0; text-align:center; }
.distribution-caption { margin:0 0 5px; color:#f6d399; font-size:15px; line-height:1.5; }
.distribution-source { position:relative; display:flex; align-items:center; justify-content:center; gap:12px; padding:62px 4px 18px; }
.distribution-factor { font-size:29px; background:#604722; color:#ffdc9a; border:1px solid #ccab70; border-radius:10px; padding:9px 13px; flex-shrink:0; }
.distribution-group { display:flex; align-items:center; gap:8px; min-width:0; }
.distribution-paren { font:45px Georgia,serif; color:#86a6c3; }
.distribution-targets { display:flex; flex-wrap:wrap; align-items:center; justify-content:center; gap:10px; }
.distribution-target { font-size:29px; color:#b9edf3; border:1px solid #7396ae; border-radius:8px; padding:9px 12px; transition:background .2s,box-shadow .2s; }
.distribution-times, .distribution-plus { font-size:24px; color:#9eb9d1; }
.receiving-factor { background:#245b68; box-shadow:0 0 0 3px #e9bd7955; border-color:#ffd48a; }
.distributed-target { background:#163f4c; }
.distribution-arrows { position:absolute; left:0; top:0; width:100%; height:100%; overflow:visible; pointer-events:none; }
.distribution-arrows path { stroke:#f4c878; stroke-width:2; fill:none; opacity:.85; }
.flying-factor { position:absolute; transform:translate(-50%,-100%); padding:4px 8px; border:1px solid #ffda91; border-radius:7px; background:#644b28; color:#ffe4af; font-size:23px; box-shadow:0 3px 12px #0005; pointer-events:none; }
.distribution-products { display:flex; justify-content:center; align-items:center; flex-wrap:wrap; gap:12px; min-height:80px; }
.distribution-product.term { cursor:default; padding:10px 14px; font-size:28px; }
@media(max-width:520px) {
  .equation-stage.distributing { padding:20px 12px; }
  .distribution-factor,.distribution-target { font-size:22px; padding:8px; }
  .distribution-source { gap:6px; }
  .distribution-group,.distribution-targets { gap:5px; }
  .distribution-paren { font-size:35px; }
  .distribution-product.term { font-size:23px; }
  .distribution-caption { font-size:14px; }
  .flying-factor { font-size:20px; }
}
.term.constant {
  color:#f2f6fe;
  background:linear-gradient(150deg,#3c5068,#273b52);
  border-color:#a0b3ce60
}
.term:hover {
  border-color:#c8f9ff;
  box-shadow:inset 0 1px 0 #fff3,0 4px 0 #071827,0 0 0 3px #80e9ff18;
  transform:translateY(-2px)
}
.term.selected {
  border-color:#f3bf5d;
  box-shadow:0 0 0 3px #f3bf5d77,0 6px 12px #0003
}
.term .math {
  pointer-events:none
}
.math {
  font-family:Cambria,"Times New Roman",serif;
  display:inline-flex;
  align-items:center;
  justify-content:center;
  gap:.12em;
  line-height:1.25;
  white-space:nowrap
}
.math.variable {
  font-style:italic
}
.math.sum,.math.product {
  gap:.19em
}
.math.negative {
  gap:.1em
}
.math.fraction {
  display:inline-flex;
  flex-direction:column;
  vertical-align:middle;
  gap:0;
  font-size:.85em
}
.fraction>.numerator {
  padding:0 .16em .08em;
  border-bottom:1.5px solid currentColor;
  width:100%;
  text-align:center;
  display:flex;
  justify-content:center
}
.fraction>.denominator {
  padding:.08em .16em 0
}
.paren {
  font-weight:400;
  opacity:.85
}
.plus-sign {
  font-size:23px;
  color:#9bb2ca;
  font-family:Georgia,serif
}
.term .math.product>.math.variable {
  margin-left:.04em
}
.operation-echo {
  position:absolute;
  left:24px;
  right:24px;
  bottom:11px;
  display:grid;
  grid-template-columns:1fr 38px 1fr;
  gap:14px;
  pointer-events:none;
  color:#f2c16c;
  font-size:24px;
  text-align:center
}
.echo-side {
  display:flex;
  align-items:center;
  justify-content:center;
  gap:8px
}
.ghost-term {
  position:fixed;
  pointer-events:none;
  z-index:30;
  margin:0
}
.ghost-term.cancelled:after {
  content:"";
  height:2px;
  background:#ffb59e;
  position:absolute;
  inset:50% 7px auto;
  transform:rotate(-12deg)
}
.selection-bar {
  min-height:51px;
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:10px;
  padding:12px 26px;
  color:#b2c6d9;
  font-size:14px;
  border-top:1px solid #bedcf215;
  background:#0a1a2d55
}
.selection-actions {
  display:flex;
  flex-wrap:wrap;
  align-items:center;
  gap:8px
}
.selection-expression {
  display:inline-flex;
  vertical-align:middle;
  margin-left:6px;
  color:#f8dca1;
  font-size:19px;
  max-width:100%;
  overflow-x:auto
}
.selection-actions .text-button:not(#clear-selection) {
  border:1px solid #7caa9e;
  border-radius:7px;
  padding:8px 10px;
  min-height:44px;
  color:#bcf0db
}
.selection-actions .text-button:hover {
  background:#244960
}
.text-button {
  border:0;
  background:none;
  color:#bbddfa;
  padding:3px 5px;
  font-size:13px
}
.action-row {
  display:flex;
  gap:10px;
  padding:18px 26px 8px
}
.board-button {
  color:#e3f1ff;
  background:#18344f;
  border:1px solid #456078;
  border-radius:9px;
  min-height:44px;
  padding:9px 15px;
  font-size:14px
}
.board-button:hover:not(:disabled) {
  background:#244960;
  border-color:#7895ac
}
.board-button>span {
  margin-right:6px;
  color:#9edfed;
  font-size:18px
}
.hint-button {
  margin-left:auto;
  background:transparent;
  border-color:transparent;
  color:#a9d4ef
}
.operation-form {
  padding:16px 26px 24px
}
.operation-form>label {
  display:block;
  font-size:12px;
  letter-spacing:.5px;
  font-weight:700;
  color:#b2c6d9;
  margin-bottom:9px
}
.operation-fields {
  display:flex;
  gap:9px
}
.operation-fields input,.operation-fields select {
  color:#eef5ff;
  background:#071a2d;
  border:1px solid #527088;
  border-radius:9px;
  padding:12px 13px;
  font-size:16px
}
.operation-fields select {
  flex:0 1 175px
}
.operation-fields input {
  flex:1;
  width:100px
}
.operation-fields input::placeholder {
  color:#a3b9cd
}
.apply {
  border:1px solid #a6f4fc;
  background:#99e5ef;
  color:#09263b;
  border-radius:9px;
  padding:10px 23px
}
.apply:hover {
  background:#bef5fa
}
.apply span {
  padding-left:13px
}
.operation-form .error {
  color:#ffb8ad
}
.hint-panel {
  display:flex;
  align-items:center;
  gap:18px;
  margin:0 26px 23px;
  padding:15px 17px;
  border-radius:10px;
  background:#19344b;
  border-left:3px solid #f3c574
}
.hint-panel p {
  font-size:15px;
  line-height:1.55;
  margin:0;
  flex:1
}
.hint-panel button {
  font-size:13px;
  padding:9px 12px;
  white-space:nowrap;
  background:#f3c574;
  border:0;
  border-radius:7px;
  color:#243348
}
.result:empty {
  display:none
}
.result {
  padding:17px 26px;
  background:#124442;
  border-top:1px solid #60bc994d;
  color:#b8f3d8;
  font-size:16px;
  line-height:1.5
}
.result[data-kind=contradiction] {
  background:#4a3332;
  color:#ffd7bc
}
.result[data-kind=identity] {
  background:#173b56;
  color:#c0e5ff
}
.steps-panel {
  border:1px solid var(--line);
  background:#fff;
  border-radius:var(--radius);
  padding:23px 23px 12px;
  min-width:0;
  max-height:710px;
  overflow:auto
}
.steps-heading {
  display:flex;
  justify-content:space-between;
  align-items:center;
  gap:8px
}
.steps-heading h2 {
  font-size:17px;
  letter-spacing:-.3px;
  margin:0
}
.steps-heading span {
  font-size:12px;
  color:var(--muted)
}
.steps-intro {
  font-size:13px;
  line-height:1.55;
  color:var(--muted);
  margin:10px 0 20px
}
#steps {
  list-style:none;
  padding:0;
  margin:0;
  counter-reset:steps
}
#steps li {
  position:relative;
  padding:0 0 24px 23px;
  border-left:1px solid #dae4ef;
  margin-left:5px
}
#steps li:before {
  content:"";
  position:absolute;
  width:9px;
  height:9px;
  border-radius:50%;
  background:#bbcde0;
  left:-5px;
  top:4px;
  box-shadow:0 0 0 4px white
}
#steps li:last-child {
  border-left-color:transparent
}
#steps li.current:before {
  background:var(--blue)
}
.step-label {
  font-size:12px;
  color:var(--muted);
  line-height:1.5;
  margin:0 0 9px
}
.step-equation {
  display:flex;
  align-items:center;
  flex-wrap:wrap;
  gap:5px;
  font-size:19px;
  overflow-wrap:anywhere;
  line-height:1.5;
  color:#304c69
}
.step-equation>.history-side {
  display:inline-flex;
  align-items:center;
  gap:4px;
  flex-wrap:wrap;
  max-width:100%
}
.step-equation .math {
  white-space:normal
}
.step-equation .math.sum {
  flex-wrap:wrap
}
.current .step-equation {
  color:#124f99
}
.workspace-footer {
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:16px;
  margin-top:22px;
  font-size:12px;
  color:var(--muted)
}
.workspace-footer>span:first-child {
  display:flex;
  align-items:center;
  gap:8px
}
.legend {
  width:9px;
  height:9px;
  border-radius:3px;
  display:inline-block
}
.variable-legend {
  background:#318b9e
}
.number-legend {
  background:#8495aa;
  margin-left:12px
}
body.presenting .entry,body.presenting .workspace-footer,body.presenting .workspace-label {
  display:none
}
body.presenting main {
  max-width:1800px
}
body.presenting .workspace-grid {
  grid-template-columns:minmax(0,1fr) 350px
}
body.presenting .equation-stage {
  min-height:390px
}
body.presenting .term {
  font-size:38px;
  min-height:85px
}
.board.solved .term {
  border-color:#81d6b0
}
.board.solved #goal {
  color:#a0e8c4
}
@media(min-width:1500px) {
  .term {
  font-size:33px
}
.equation-stage {
  min-height:325px
}
}
@media(max-width:1100px) {
  .workspace-grid,body.presenting .workspace-grid {
  grid-template-columns:minmax(0,1fr) 260px
}
.term {
  font-size:25px;
  padding:10px 12px
}
.entry-footer {
  align-items:flex-start
}
.entry-heading>span {
  display:none
}
.board-heading>div:first-child {
  align-items:flex-start;
  flex-direction:column;
  gap:5px
}
}
@media(max-width:850px) {
  .workspace-grid,body.presenting .workspace-grid {
  grid-template-columns:1fr
}
.steps-panel {
  max-height:none
}
.entry-footer {
  flex-direction:column;
  gap:6px
}
.workspace-label {
  display:none
}
.equation-stage {
  min-height:270px
}
.board-heading>div:first-child {
  flex-direction:row;
  align-items:center;
  gap:15px
}
.steps-panel {
  padding:22px
}
#steps {
  display:flex;
  overflow-x:auto;
  gap:18px
}
#steps li {
  min-width:190px;
  border-left:0;
  padding-left:16px;
  max-width:400px
}
.term {
  font-size:29px
}
.workspace-footer {
  align-items:flex-start
}
.workspace-footer>span:last-child {
  max-width:150px;
  text-align:right
}
}
@media(max-width:520px) {
  .topbar {
  padding:0 16px;
  height:64px
}
.brand {
  font-size:16px
}
.quiet {
  padding:8px 12px;
  font-size:13px
}
main {
  padding:16px 10px
}
.entry {
  padding:18px 16px;
  margin-bottom:15px
}
h1 {
  font-size:20px
}
#equation-form {
  flex-direction:column;
  gap:10px
}
#equation-input {
  font-size:21px;
  padding:13px;
  width:100%
}
.primary {
  padding:12px
}
.entry-footer p {
  font-size:12px
}
.board-heading {
  padding:17px
}
.eyebrow {
  display:none
}
.history-controls span {
  display:none
}
.history-controls button {
  padding:5px 12px
}
.equation-stage {
  padding:57px 12px 50px;
  min-height:260px
}
.equation {
  gap:6px;
  grid-template-columns:minmax(0,1fr) 23px minmax(0,1fr)
}
.equals {
  font-size:31px
}
.term {
  min-height:57px;
  padding:9px;
  font-size:25px;
  border-radius:9px
}
.equation-side {
  gap:9px 5px
}
.plus-sign {
  font-size:20px
}
.selection-bar {
  padding:12px 17px;
  line-height:1.5
}
.action-row {
  padding:14px 14px 5px;
  gap:6px;
  flex-wrap:wrap
}
.board-button {
  padding:8px 10px;
  font-size:13px
}
.hint-button {
  margin-left:0;
  flex:1
}
.operation-form {
  padding:15px 17px 20px
}
.operation-fields {
  gap:7px;
  flex-wrap:wrap
}
.operation-fields select {
  flex:0 1 135px;
  font-size:15px;
  padding:10px
}
.operation-fields input {
  width:100px;
  padding:10px;
  font-size:16px
}
.apply {
  flex-basis:100%;
  padding:11px
}
.hint-panel {
  margin:0 17px 17px;
  flex-direction:column;
  align-items:stretch;
  gap:10px
}
.workspace-footer {
  font-size:11px;
  gap:10px
}
.workspace-footer>span:first-child {
  gap:5px
}
.number-legend {
  margin-left:4px
}
.result {
  padding:15px 17px
}
.workspace-grid {
  gap:16px
}
body.presenting .term {
  font-size:27px;
  min-height:65px
}
}
@media(prefers-reduced-motion:reduce) {
  *,*:before,*:after {
  animation:none!important;
  transition:none!important;
  scroll-behavior:auto!important
}
}