* { box-sizing: border-box; }

.main-content *,
.main-content *::before,
.main-content *::after {
  box-sizing: border-box;
}

.main-content button,
.main-content input,
.main-content select {
  font: inherit;
}

.main-content :focus-visible {
  outline: 3px solid var(--kw-accent);
  outline-offset: 3px;
}

.intro-note {
  max-width: 760px;
  margin: 12px 0 0;
  padding-left: 12px;
  border-left: 3px solid var(--kw-line-strong);
  color: var(--kw-muted);
  font-size: 0.86rem;
}

.intro > h1 {
  text-wrap: balance;
}

.intro > h1 .no-break {
  white-space: nowrap;
}

.section-kicker {
  margin: 0 0 5px;
  color: var(--kw-accent);
  font-size: 0.76rem;
  font-weight: 750;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.section-heading {
  margin-bottom: 16px;
}

.main-content h2,
.main-content h3 {
  margin: 0;
  color: var(--kw-ink);
  line-height: 1.4;
}

.main-content h2 {
  font-size: clamp(1.18rem, 2vw, 1.48rem);
}

.main-content h3 {
  font-size: 1rem;
}

.tool-shell {
  display: grid;
  grid-template-columns: minmax(0, 0.96fr) minmax(0, 1.04fr);
  border: 1px solid var(--kw-line-strong);
  background: var(--kw-surface);
}

.calculator-panel,
.visual-panel {
  min-width: 0;
  padding: 24px;
}

.calculator-panel {
  border-right: 1px solid var(--kw-line);
}

.input-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px 12px;
}

.input-row-wide {
  grid-column: 1 / -1;
}

.input-row {
  min-width: 0;
}

.input-row label {
  display: block;
  margin-bottom: 5px;
  font-weight: 720;
}

.input-wrap {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  align-items: stretch;
}

.input-wrap input {
  width: 100%;
  min-width: 0;
  min-height: 44px;
  padding: 9px 10px;
  border: 1px solid var(--kw-line-strong);
  border-right: 0;
  border-radius: 2px 0 0 2px;
  color: var(--kw-ink);
  background: #fff;
  font-variant-numeric: tabular-nums;
}

.input-wrap .unit-select {
  min-width: 82px;
  min-height: 44px;
  padding: 7px 25px 7px 9px;
  border: 1px solid var(--kw-line-strong);
  border-radius: 0 2px 2px 0;
  background: var(--kw-paper);
  color: var(--kw-ink);
  cursor: pointer;
  font-size: 0.82rem;
  font-weight: 700;
}

.input-wrap input + .unit-select {
  border-left: 0;
}

.input-wrap input[aria-invalid="true"] {
  border-color: #9b2f2f;
  background: #fff8f8;
}

.input-wrap select:focus-visible,
.input-wrap input:focus-visible {
  position: relative;
  z-index: 1;
}

.unit-label {
  display: grid;
  min-width: 48px;
  min-height: 44px;
  place-items: center;
  padding: 7px 9px;
  border: 1px solid var(--kw-line-strong);
  border-radius: 0 2px 2px 0;
  background: var(--kw-paper);
  color: var(--kw-muted);
  font-size: 0.78rem;
  font-weight: 700;
  white-space: nowrap;
}

.field-help,
.field-error {
  margin: 4px 0 0;
  font-size: 0.76rem;
  line-height: 1.45;
}

.field-help {
  color: var(--kw-muted);
}

.field-error {
  min-height: 1.1em;
  color: #8b2929;
}

.form-error {
  margin: 14px 0 0;
  padding: 9px 11px;
  border-left: 4px solid #9b2f2f;
  background: #f8e9e7;
  color: #762525;
}

.form-error[hidden] {
  display: none;
}

.form-actions {
  display: flex;
  gap: 8px;
  margin-top: 16px;
}

.button {
  min-height: 44px;
  padding: 9px 16px;
  border: 1px solid var(--kw-accent);
  border-radius: 2px;
  cursor: pointer;
  font-weight: 760;
}

.button-primary {
  background: var(--kw-accent);
  color: #fff;
}

.button-secondary {
  background: var(--kw-surface);
  color: var(--kw-accent);
}

.button:hover {
  border-color: var(--kw-ink);
}

.result-box {
  margin-top: 20px;
  padding: 16px;
  border: 1px solid var(--kw-accent);
  border-left-width: 4px;
  background: var(--kw-accent-soft);
}

.result-box[data-state="error"] {
  border-color: #9b2f2f;
  background: #f8e9e7;
}

.result-label {
  margin: 0;
  color: var(--kw-accent);
  font-size: 0.78rem;
  font-weight: 780;
}

.result-box[data-state="error"] .result-label {
  color: #8b2929;
}

.result-value {
  display: block;
  margin-top: 3px;
  color: var(--kw-ink);
  font-size: clamp(1.36rem, 2.8vw, 1.9rem);
  font-weight: 780;
  font-variant-numeric: tabular-nums;
  line-height: 1.3;
  overflow-wrap: anywhere;
}

.result-secondary {
  margin: 2px 0 0;
  color: var(--kw-ink);
  font-size: 1.05rem;
  font-weight: 730;
  font-variant-numeric: tabular-nums;
}

.result-status {
  margin: 7px 0 0;
  color: #3f4c46;
  font-size: 0.88rem;
}

.result-details {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  margin: 14px 0 0;
  border-top: 1px solid rgb(36 91 73 / 35%);
  border-left: 1px solid rgb(36 91 73 / 35%);
}

.result-details[hidden] {
  display: none;
}

.result-details > div {
  min-width: 0;
  padding: 9px 10px;
  border-right: 1px solid rgb(36 91 73 / 35%);
  border-bottom: 1px solid rgb(36 91 73 / 35%);
}

.result-details .detail-wide {
  grid-column: 1 / -1;
}

.result-details dt {
  color: var(--kw-muted);
  font-size: 0.75rem;
  font-weight: 750;
}

.result-details dd {
  margin: 2px 0 0;
  font-size: 0.86rem;
  font-weight: 650;
  overflow-wrap: anywhere;
  white-space: pre-wrap;
}

.visual-heading-row {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 12px;
}

.status-badge {
  flex: 0 0 auto;
  padding: 4px 8px;
  border: 1px solid var(--kw-line-strong);
  background: var(--kw-paper);
  color: var(--kw-muted);
  font-size: 0.74rem;
  font-weight: 750;
}

.status-badge[data-state="ready"] {
  border-color: var(--kw-accent);
  background: var(--kw-accent-soft);
  color: var(--kw-accent);
}

.status-badge[data-state="error"] {
  border-color: #9b2f2f;
  background: #f8e9e7;
  color: #8b2929;
}

.visual-metrics {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  margin: 15px 0 0;
  border-top: 1px solid var(--kw-line);
  border-left: 1px solid var(--kw-line);
}

.visual-metrics > div {
  min-width: 0;
  padding: 8px 9px;
  border-right: 1px solid var(--kw-line);
  border-bottom: 1px solid var(--kw-line);
}

.visual-metrics dt {
  color: var(--kw-muted);
  font-size: 0.72rem;
  font-weight: 750;
}

.visual-metrics dd {
  margin: 2px 0 0;
  font-size: 0.82rem;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
  overflow-wrap: anywhere;
}

.diagram-frame {
  min-height: 330px;
  margin-top: 15px;
  overflow: hidden;
  border: 1px solid var(--kw-line-strong);
  background: linear-gradient(180deg, #fbfaf6 0%, #edf2ef 100%);
}

.coulomb-diagram {
  display: block;
  width: 100%;
  height: auto;
  min-height: 330px;
  font-family: var(--kw-font);
}

.diagram-charge {
  stroke: #27343d;
  stroke-width: 3;
}

.diagram-charge-positive {
  fill: #e2ebe5;
}

.diagram-charge-negative {
  fill: #f8e9e7;
}

.diagram-charge-zero {
  fill: #f5f4ef;
}

.diagram-force,
.diagram-field {
  fill: none;
  stroke-linecap: round;
}

.diagram-force {
  stroke: #a04a37;
  stroke-width: 5;
}

.diagram-field {
  stroke: #34718c;
  stroke-width: 4;
}

.diagram-distance {
  stroke: #687069;
  stroke-width: 2;
  stroke-dasharray: 5 5;
}

.diagram-axis {
  stroke: #9fa79f;
  stroke-width: 2;
  stroke-dasharray: 5 5;
}

.diagram-charge-text {
  fill: #222824;
  font-size: 18px;
  font-weight: 800;
  text-anchor: middle;
}

.diagram-label {
  fill: #222824;
  font-size: 17px;
  font-weight: 700;
  text-anchor: middle;
}

.diagram-value {
  fill: #3f4c46;
  font-size: 14px;
  text-anchor: middle;
}

.diagram-direction {
  fill: #245b49;
  font-size: 16px;
  font-weight: 750;
  text-anchor: middle;
}

.diagram-muted {
  fill: #687069;
  font-size: 16px;
}

.diagram-zero {
  fill: #687069;
  font-size: 15px;
  font-weight: 700;
  text-anchor: middle;
}

.diagram-coil {
  fill: none;
  stroke: #27343d;
  stroke-width: 5;
}

.diagram-axis {
  stroke: #687069;
  stroke-width: 2;
  stroke-dasharray: 5 5;
}

.diagram-normal {
  stroke: #245b49;
  stroke-width: 3;
}

.diagram-field-initial,
.diagram-field-final {
  stroke-width: 3;
}

.diagram-field-initial {
  stroke: #34718c;
}

.diagram-field-final {
  stroke: #a04a37;
}

.diagram-current {
  fill: none;
  stroke: #245b49;
  stroke-width: 5;
}

.diagram-muted {
  fill: #687069;
  font-size: 16px;
}

.diagram-label {
  fill: #222824;
  font-size: 18px;
  font-weight: 700;
  text-anchor: middle;
}

.diagram-value {
  fill: #3f4c46;
  font-size: 15px;
  text-anchor: middle;
}

.diagram-direction {
  fill: #245b49;
  font-size: 16px;
  font-weight: 750;
  text-anchor: middle;
}

.visual-description {
  margin: 11px 0 0;
  color: #38413b;
  font-size: 0.88rem;
}

.scale-note {
  margin: 7px 0 0;
  padding-left: 11px;
  border-left: 3px solid var(--kw-line-strong);
  color: var(--kw-muted);
  font-size: 0.77rem;
}

.content-section {
  margin-top: 30px;
  padding-top: 25px;
  border-top: 1px solid var(--kw-line-strong);
}

.steps-list {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  margin: 0;
  padding: 0;
  counter-reset: step;
  list-style: none;
}

.steps-list li {
  min-width: 0;
  padding: 12px 13px;
  border: 1px solid var(--kw-line);
  border-right: 0;
  color: var(--kw-muted);
  font-size: 0.86rem;
}

.steps-list li:last-child {
  border-right: 1px solid var(--kw-line);
}

.steps-list li::before {
  display: block;
  margin-bottom: 4px;
  color: var(--kw-accent);
  font-size: 0.75rem;
  font-weight: 780;
  content: "0" counter(step);
  counter-increment: step;
}

.formula-list {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  border-top: 1px solid var(--kw-line);
  border-left: 1px solid var(--kw-line);
}

.formula-list article {
  min-width: 0;
  display: grid;
  gap: 4px;
  padding: 12px 13px;
  border-right: 1px solid var(--kw-line);
  border-bottom: 1px solid var(--kw-line);
}

.formula-list strong {
  overflow-wrap: anywhere;
}

.formula-list span {
  color: var(--kw-muted);
  font-size: 0.84rem;
}

.assumption-panel {
  margin-top: 18px;
  border: 1px solid var(--kw-line);
}

.assumption-panel h3 {
  padding: 10px 13px;
  border-bottom: 1px solid var(--kw-line);
  color: var(--kw-accent);
}

.assumption-panel ul {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  margin: 0;
  padding: 0;
  list-style: none;
}

.assumption-panel li {
  padding: 10px 13px 10px 30px;
  border-right: 1px solid var(--kw-line);
  border-bottom: 1px solid var(--kw-line);
  color: var(--kw-muted);
  font-size: 0.84rem;
}

.assumption-panel li:nth-child(2n) {
  border-right: 0;
}

.assumption-panel li:nth-last-child(-n + 2) {
  border-bottom: 0;
}

.assumption-panel li::before {
  margin-left: -17px;
  margin-right: 7px;
  color: var(--kw-accent);
  content: "—";
}

@media (max-width: 920px) {
  .tool-shell {
    grid-template-columns: 1fr;
  }

  .calculator-panel {
    border-right: 0;
    border-bottom: 1px solid var(--kw-line);
  }

  .steps-list,
  .formula-list {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .steps-list li:nth-child(2) {
    border-right: 1px solid var(--kw-line);
  }

  .steps-list li:nth-child(n + 3) {
    border-top: 0;
  }
}

@media (max-width: 640px) {
  .calculator-panel,
  .visual-panel {
    padding: 17px 14px;
  }

  .input-grid,
  .result-details,
  .visual-metrics,
  .steps-list,
  .formula-list,
  .assumption-panel ul {
    grid-template-columns: 1fr;
  }

  .form-actions {
    display: grid;
    grid-template-columns: 1fr;
  }

  .button {
    width: 100%;
  }

  .result-details .detail-wide {
    grid-column: auto;
  }

  .steps-list li,
  .steps-list li:nth-child(2) {
    border-top: 0;
    border-right: 1px solid var(--kw-line);
  }

  .steps-list li:first-child {
    border-top: 1px solid var(--kw-line);
  }

  .assumption-panel li,
  .assumption-panel li:nth-child(2n),
  .assumption-panel li:nth-last-child(-n + 2) {
    border-right: 0;
    border-bottom: 1px solid var(--kw-line);
  }

  .assumption-panel li:last-child {
    border-bottom: 0;
  }

  .diagram-frame,
  .coulomb-diagram {
    min-height: 280px;
  }
}

@media (prefers-reduced-motion: reduce) {
  .main-content *,
  .main-content *::before,
  .main-content *::after {
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
  }
}