/* Algebra concreta | Stile nativo accessibile del laboratorio.
 * Data: 2026-11-04 | Release: non definita | Licenza: non definita.
 * Autore: Leonardo Teatini.
 * Design read: prodotto didattico calmo e concreto. DESIGN_VARIANCE 3,
 * MOTION_INTENSITY 2, VISUAL_DENSITY 3. Tema chiaro, accento verde unico.
 * Principi pertinenti di design-taste-frontend; nessun sistema UI esterno.
 */
:root { color-scheme: light; --ink:#20342f; --muted:#52665f; --accent:#176052; --accent-soft:#eaf3ef; --paper:#f5f7f4; --line:#cbd6cf; --radius:12px; font-family:"Segoe UI",Arial,sans-serif; font-size:18px; line-height:1.5; color:var(--ink); background:var(--paper); }
* { box-sizing:border-box; }
body { margin:0; min-height:100dvh; }
button,input,select { font:inherit; }
button,a,input,select { -webkit-tap-highlight-color:transparent; }
button { cursor:pointer; }
a { color:var(--accent); }
button,input,select { border-radius:var(--radius); }
button { min-height:48px; border:1px solid var(--line); background:#fff; color:var(--ink); padding:.65rem 1rem; font-weight:600; }
button:hover { border-color:var(--accent); background:var(--accent-soft); }
button:active { transform:translateY(1px); }
button:disabled { cursor:default; background:#e8ede9; color:#53635c; border-color:var(--line); }
:focus-visible { outline:3px solid var(--accent); outline-offset:4px; }
input,select { border:1px solid #71877c; background:#fff; color:var(--ink); min-height:48px; padding:.55rem .7rem; }
input[type="number"] { width:6.5rem; }
input[type="radio"],input[type="checkbox"] { min-height:auto; width:22px; height:22px; accent-color:var(--accent); flex-shrink:0; }
h1,h2,h3,p { margin-top:0; }
h1 { font-size:clamp(1.7rem,3vw,2rem); line-height:1.18; letter-spacing:-.025em; font-weight:650; margin-bottom:.65rem; max-width:36ch; }
h2 { font-size:1.25rem; line-height:1.3; margin-bottom:.6rem; }
h3 { font-size:1.05rem; }
p { max-width:64ch; }
small,.small { font-size:.88rem; }
.muted { color:var(--muted); }
.primary { color:#fff; background:var(--accent); border-color:var(--accent); }
.primary:hover { color:#fff; background:#114b40; }
.text-button { border-color:transparent; background:transparent; color:var(--accent); }
.button-row { display:flex; align-items:center; flex-wrap:wrap; gap:.65rem; margin-top:1.25rem; }
.site-header { max-width:1200px; margin:auto; padding:0 2rem; height:80px; display:flex; align-items:center; justify-content:space-between; gap:1rem; }
.brand { display:flex; align-items:center; gap:.7rem; text-decoration:none; color:var(--ink); font-weight:700; white-space:nowrap; }
.brand-mark { display:grid; place-items:center; width:36px; height:36px; background:var(--accent); color:#fff; border-radius:8px; font-size:1.5rem; font-weight:600; }
nav { display:flex; gap:.25rem; }
nav button { background:transparent; border-color:transparent; font-size:.9rem; white-space:nowrap; }
nav button[aria-current="page"] { background:var(--accent-soft); color:var(--accent); }
main { max-width:1130px; margin:0 auto; padding:2rem 1rem 2.5rem; min-height:calc(100dvh - 150px); }
main:focus { outline:none; }
.activity-heading { display:flex; justify-content:space-between; align-items:start; gap:1.5rem; margin-bottom:1.5rem; }
.activity-heading p { margin-bottom:0; color:var(--muted); }
.steps { list-style:none; display:flex; padding:0; margin:0 0 1rem; gap:1.4rem; font-size:.85rem; color:var(--muted); }
.steps li { display:flex; align-items:center; gap:.4rem; }
.steps li::before { content:attr(data-step); width:24px; height:24px; display:grid; place-items:center; border:1px solid var(--line); border-radius:50%; font-size:.72rem; }
.steps li[aria-current="step"] { color:var(--accent); font-weight:650; }
.steps li[aria-current="step"]::before { background:var(--accent); border-color:var(--accent); color:#fff; }
.intro { padding-top:1.5rem; }
.intro-copy { margin-bottom:1.5rem; }
.intro-copy p { max-width:52ch; color:var(--muted); }
.lab { background:#fff; border:1px solid var(--line); border-radius:var(--radius); overflow:hidden; }
.concrete-board { display:grid; grid-template-columns:1fr 64px 1fr; padding:.8rem 2rem; align-items:stretch; gap:.65rem; min-height:180px; }
.side { display:flex; flex-direction:column; align-items:center; justify-content:center; min-width:0; }
.side-title { color:var(--muted); font-size:.85rem; margin:0 0 .5rem; }
.objects { display:flex; justify-content:center; align-items:center; flex-wrap:wrap; gap:12px; min-height:90px; }
.object-plus { font-size:1.5rem; color:var(--muted); margin:0 .1rem; }
.context-controls { display:flex; align-items:end; flex-wrap:wrap; gap:1rem; margin-bottom:1.5rem; }
.context-controls .field { flex:1; min-width:180px; }
.units { display:grid; grid-template-columns:repeat(5,52px); justify-content:center; align-items:center; gap:8px; max-width:100%; }
.unit { display:grid; place-items:center; width:52px; height:66px; min-height:0; padding:0; border:0; background:transparent; border-radius:8px; }
.unit img { width:100%; height:100%; object-fit:contain; user-select:none; }
.units.selectable { grid-template-columns:repeat(3,56px); gap:8px; }
button.unit { width:56px; height:72px; min-height:48px; border:1px solid var(--line); background:#fff; }
button.unit[aria-pressed="true"] { outline:3px solid var(--accent); outline-offset:2px; background:var(--accent-soft); }
.item-persona .unit { height:90px; }
.item-banconota-euro { grid-template-columns:repeat(3,86px); }
.item-banconota-euro .unit { width:86px; height:50px; }
.item-banconota-euro.selectable { grid-template-columns:repeat(3,86px); }
.container-object { width:110px; height:104px; position:relative; flex-shrink:0; }
.container-object img { width:100%; height:100%; object-fit:contain; user-select:none; }
.container-object span { position:absolute; left:50%; top:50%; transform:translate(-50%,-50%); font-size:1.7rem; font-weight:750; background:transparent; color:var(--ink); border:0; text-align:center; line-height:1.2; text-shadow:1px 1px 0 #fff,-1px 1px 0 #fff,1px -1px 0 #fff,-1px -1px 0 #fff; }
.container-furgone { width:145px; height:104px; }
.container-zaino { width:94px; height:114px; }
.container-busta { width:118px; height:94px; }
.equal-sign { align-self:center; font-size:2.6rem; font-weight:400; text-align:center; color:var(--accent); }
.equal-sign span { background:#fff; position:relative; padding:0 5px; z-index:1; }
.balance-view { position:relative; }
.balance-view .concrete-board { padding-top:112px; padding-bottom:72px; }
.balance-beam { position:absolute; top:80px; left:16%; right:16%; height:5px; background:var(--accent); border-radius:3px; transform-origin:center; }
.balance-view .side { position:relative; padding-bottom:22px; }
.balance-view .side::before { content:""; width:2px; height:32px; position:absolute; top:-32px; left:50%; background:#71877c; }
.balance-view .side::after { content:""; position:absolute; bottom:0; left:5%; right:5%; height:15px; border-bottom:5px solid var(--accent); border-radius:0 0 30% 30%; }
.balance-view .equal-sign { align-self:stretch; display:flex; justify-content:center; align-items:center; position:relative; }
.balance-view .equal-sign::before { content:""; position:absolute; top:-32px; bottom:-52px; left:calc(50% - 3px); width:6px; background:var(--accent); }
.balance-view .equal-sign::after { content:""; position:absolute; bottom:-52px; width:54px; height:6px; background:var(--accent); border-radius:3px; }
.balance-note { text-align:center; font-size:.8rem; color:var(--muted); padding:0 .7rem; margin:.6rem auto; }
.operation-tag { display:block; background:var(--accent-soft); color:var(--accent); border:1px solid var(--accent); border-radius:6px; font-size:1.2rem; font-weight:700; padding:0 .6rem; margin-top:.5rem; }
.transition-instruction { margin:.5rem 0 1rem; color:var(--accent); }
.transition-instruction p { margin-bottom:0; }
.equation-arrow { font-size:.8em; }
.division-groups { display:flex; flex-wrap:wrap; justify-content:center; gap:8px; }
.division-group { border:2px dashed var(--accent); background:var(--accent-soft); padding:.5rem; border-radius:8px; animation:group-in 1.1s ease-out both; }
.division-group .units { grid-template-columns:repeat(3,40px); gap:4px; }
.division-group .unit { width:40px; height:52px; }
.division-group .container-object { width:76px; height:76px; }
.division-group .item-banconota-euro { grid-template-columns:repeat(2,64px); }
.division-group .item-banconota-euro .unit { width:64px; height:42px; }
.group-caption { display:block; text-align:center; font-size:.75rem; color:var(--accent); margin-bottom:.3rem; }
.unit-removing { animation:take-away 1.25s ease-in both; }
@keyframes take-away { 0%,20% { opacity:1; transform:translateY(0); } 100% { opacity:0; transform:translateY(-35px); } }
@keyframes group-in { from { opacity:.3; transform:translateY(8px); } to { opacity:1; transform:translateY(0); } }
.error-feedback { display:flex; align-items:flex-start; gap:1rem; }
.error-cross { color:#b32026; font-size:5rem; line-height:.85; font-weight:700; flex-shrink:0; }
.object-caption { font-size:.8rem; margin:.5rem 0 0; color:var(--muted); text-align:center; }
.equation { border-top:1px solid var(--line); text-align:center; padding:.65rem; font-size:2rem; line-height:1.4; font-weight:600; letter-spacing:.025em; font-variant-numeric:tabular-nums; background:#fafcf9; }
.exercise-equation-reminder { display:none; }
.meaning { text-align:center; font-size:.88rem; color:var(--muted); margin:.8rem auto 1.1rem; max-width:100%; }
.instruction { margin:1.5rem 0 .75rem; }
.example-text { min-height:3rem; font-size:1.05rem; max-width:65ch; }
.example-controls { display:flex; align-items:center; justify-content:space-between; gap:1rem; margin-top:1rem; }
.example-position { font-size:.85rem; color:var(--muted); }
.operation-form { display:grid; grid-template-columns:1fr 1fr; gap:1.25rem 2rem; padding-top:1.1rem; border-top:1px solid var(--line); }
.operation-fields { display:flex; flex-wrap:wrap; align-items:end; gap:.75rem; }
.field { display:grid; gap:.4rem; }
.field label { font-size:.9rem; font-weight:600; }
fieldset { padding:0; margin:0; border:0; min-width:0; }
legend { font-size:.9rem; font-weight:600; padding:0 0 .5rem; }
.target-options { display:flex; gap:.4rem; flex-wrap:wrap; }
.target-options label { display:flex; align-items:center; gap:.45rem; padding:.55rem .6rem; border:1px solid var(--line); border-radius:var(--radius); min-height:48px; cursor:pointer; font-size:.9rem; }
.target-options label:has(input:checked) { border-color:var(--accent); background:var(--accent-soft); }
.form-actions { grid-column:1/-1; display:flex; align-items:center; flex-wrap:wrap; gap:.6rem; }
.feedback { background:var(--accent-soft); border-left:4px solid var(--accent); padding:1rem 1.2rem; border-radius:0 var(--radius) var(--radius) 0; margin:1.25rem 0; }
.feedback p:last-child { margin-bottom:0; }
.feedback h2 { margin-bottom:.5rem; }
.correction { border-left:4px solid #695c38; background:#f2f0e8; }
.correction-equation { font-size:1.5rem; font-weight:600; margin:.6rem 0; }
.answer-form { display:flex; align-items:end; flex-wrap:wrap; gap:.8rem; padding-top:1rem; }
.history { margin-top:1.5rem; }
summary { cursor:pointer; padding:.7rem 0; color:var(--accent); font-weight:600; }
.history ol { padding-left:1.5rem; }
.history li { padding:.3rem 0; }
.verification { background:var(--accent-soft); padding:1.5rem 2rem; border-radius:var(--radius); }
.verification .equation { border:0; background:transparent; padding:.5rem 0; text-align:left; }
.opened-boxes { display:flex; flex-wrap:wrap; gap:1rem; margin:1rem 0; }
.opened-box { border:2px solid #6d7e6c; border-top-style:dashed; border-radius:6px; padding:.9rem; background:#fff; }
.opened-box .units { grid-template-columns:repeat(3,52px); }
.opened-box .item-banconota-euro { grid-template-columns:repeat(2,86px); }
.opened-box .containers { min-height:70px; }
.opened-box p { font-size:.8rem; text-align:center; margin:.7rem 0 0; }
.notebook { padding:1.5rem 0; margin-top:.5rem; }
.notebook-equation { font-size:1.5rem; font-weight:600; }
.notebook form { display:flex; flex-wrap:wrap; align-items:end; gap:.8rem; }
.summary-intro { margin-bottom:1.75rem; }
.counts { display:grid; grid-template-columns:repeat(4,1fr); gap:1rem; margin-bottom:1.5rem; }
.count { border-top:2px solid var(--line); padding-top:.7rem; }
.count strong { font-size:2rem; font-weight:600; display:block; }
.count span { font-size:.85rem; }
.attempt-list { list-style:none; padding:0; }
.attempt-item { border-top:1px solid var(--line); padding:1rem 0; }
.attempt-top { display:flex; align-items:start; justify-content:space-between; gap:1rem; }
.attempt-top h3 { margin:0; }
.attempt-top p { margin:.25rem 0; }
.outcome { font-size:.85rem; font-weight:600; color:var(--accent); background:var(--accent-soft); padding:.3rem .6rem; border-radius:6px; }
.events { font-size:.88rem; padding-left:1.5rem; }
.events li { padding:.25rem 0; }
.events code { font:inherit; font-weight:600; }
.empty-state { padding:2rem 0; }
.site-footer { max-width:1130px; padding:1rem; margin:auto; border-top:1px solid var(--line); display:flex; flex-wrap:wrap; justify-content:space-between; align-items:center; gap:1rem; color:var(--muted); font-size:.8rem; }
.motion-toggle { display:flex; align-items:center; gap:.6rem; }
.storage-warning { max-width:1130px; margin:1rem auto; padding:1rem; border:2px solid #695c38; background:#f2f0e8; }
.skip-link { position:absolute; left:1rem; top:-100px; z-index:10; background:#fff; padding:1rem; }
.skip-link:focus { top:1rem; }
.visually-hidden { position:absolute; width:1px; height:1px; padding:0; margin:-1px; overflow:hidden; clip:rect(0,0,0,0); white-space:nowrap; border:0; }
.changed .equation { animation:step-change .35s ease-out; }
@keyframes step-change { from { background:#d3e8df; } to { background:#fafcf9; } }
.reduced-motion *, .reduced-motion *::before, .reduced-motion *::after { animation:none !important; transition:none !important; }
@media (prefers-reduced-motion:reduce) { *,*::before,*::after { animation:none !important; transition:none !important; } }
/* Nel compito attivo equazione e comandi restano vicini, senza ridurre i bersagli tattili. */
@media (min-width:641px) {
  body:has(:is(#operation-form,#operation-transition)) .site-header, body:has(#answer-form) .site-header { height:64px; }
  main:has(:is(#operation-form,#operation-transition)), main:has(#answer-form) { padding-top:.5rem; padding-bottom:1rem; }
  main:has(:is(#operation-form,#operation-transition)) .steps, main:has(#answer-form) .steps { margin-bottom:.3rem; }
  main:has(:is(#operation-form,#operation-transition)) .activity-heading, main:has(#answer-form) .activity-heading { margin-bottom:.4rem; }
  main:has(:is(#operation-form,#operation-transition)) .activity-heading h1, main:has(#answer-form) .activity-heading h1 { font-size:1.5rem; margin-bottom:.1rem; }
  main:has(:is(#operation-form,#operation-transition)) .concrete-board, main:has(#answer-form) .concrete-board { padding:.3rem 1rem; min-height:0; }
  main:has(:is(#operation-form,#operation-transition)) .balance-view .concrete-board, main:has(#answer-form) .balance-view .concrete-board { padding-top:40px; padding-bottom:22px; }
  main:has(:is(#operation-form,#operation-transition)) .balance-beam, main:has(#answer-form) .balance-beam { top:8px; }
  main:has(:is(#operation-form,#operation-transition)) .balance-view .equal-sign::before, main:has(#answer-form) .balance-view .equal-sign::before { bottom:-18px; }
  main:has(:is(#operation-form,#operation-transition)) .balance-view .equal-sign::after, main:has(#answer-form) .balance-view .equal-sign::after { bottom:-18px; }
  main:has(:is(#operation-form,#operation-transition)) .side-title, main:has(#answer-form) .side-title { margin-bottom:.1rem; }
  main:has(:is(#operation-form,#operation-transition)) .object-caption, main:has(#answer-form) .object-caption { margin-top:.1rem; }
  main:has(:is(#operation-form,#operation-transition)) .balance-note, main:has(#answer-form) .balance-note { margin:.1rem auto; }
  main:has(:is(#operation-form,#operation-transition)) .equation, main:has(#answer-form) .equation { padding:.15rem; line-height:1.2; }
  main:has(:is(#operation-form,#operation-transition)) .meaning, main:has(#answer-form) .meaning { margin:.25rem auto; }
  main:has(:is(#operation-form,#operation-transition)) .instruction, main:has(#answer-form) .instruction { margin:.4rem 0 .2rem; }
  main:has(:is(#operation-form,#operation-transition)) .instruction + p { margin-bottom:.35rem; }
  main:has(:is(#operation-form,#operation-transition)) .operation-form { padding-top:.35rem; gap:.4rem 1rem; }
  main:has(#answer-form) .answer-form { padding-top:.25rem; }
}
@media (max-width:900px) {
  .operation-form { grid-template-columns:1fr; gap:1rem; }
  .concrete-board { padding:1.5rem 1rem; }
  .units { grid-template-columns:repeat(4,52px); }
  .item-banconota-euro,.item-banconota-euro.selectable { grid-template-columns:repeat(2,86px); }
}
@media (max-width:640px) {
  :root { font-size:17px; }
  .site-header { height:auto; min-height:80px; padding:.8rem 1rem; flex-wrap:wrap; gap:.5rem; }
  nav { width:100%; }
  nav button { flex:1; }
  main { padding:1.5rem 1rem; }
  .exercise-equation-reminder { display:block; position:sticky; top:0; z-index:2; text-align:center; padding:.25rem; background:#fafcf9; border:1px solid var(--line); border-radius:var(--radius); font-size:1.5rem; font-weight:600; }
  .activity-heading { display:block; }
  .activity-heading .text-button { padding-left:0; margin-top:.5rem; }
  .steps { gap:.65rem; font-size:.8rem; }
  .concrete-board { grid-template-columns:1fr 32px 1fr; padding:1rem .5rem; gap:.2rem; min-height:230px; }
  .balance-view .concrete-board { padding-top:80px; }
  .balance-beam { top:48px; }
  .objects { gap:8px; }
  .container-object { width:74px; height:80px; }
  .container-furgone { width:120px; height:90px; }
  .container-zaino { width:68px; height:92px; }
  .container-busta { width:80px; height:68px; }
  .units { grid-template-columns:repeat(3,minmax(0,42px)); gap:4px; }
  .unit { width:100%; height:56px; }
  .units.selectable { grid-template-columns:repeat(2,50px); }
  button.unit { width:50px; height:64px; }
  .item-banconota-euro { grid-template-columns:repeat(2,minmax(0,68px)); gap:6px; }
  .item-banconota-euro .unit { width:100%; height:44px; }
  .item-banconota-euro.selectable { grid-template-columns:repeat(2,minmax(0,68px)); }
  .item-persona .unit { height:76px; }
  .division-group .units { grid-template-columns:repeat(2,32px); }
  .division-group .unit { width:32px; height:44px; }
  .division-group .container-object { width:56px; height:58px; }
  .division-group .item-banconota-euro { grid-template-columns:repeat(2,54px); }
  .division-group .item-banconota-euro .unit { width:54px; height:36px; }
  .opened-box .units { grid-template-columns:repeat(3,42px); }
  .opened-box .item-banconota-euro { grid-template-columns:repeat(2,68px); }
  .error-feedback { gap:.5rem; }
  .error-cross { font-size:4rem; }
  .object-plus { display:none; }
  .equal-sign { font-size:2rem; }
  .object-caption { font-size:.72rem; }
  .equation { font-size:1.8rem; }
  .example-controls { flex-wrap:wrap; }
  .example-controls>div { width:100%; display:flex; gap:.5rem; }
  .example-controls button { flex:1; }
  .verification { padding:1.2rem; }
  .counts { grid-template-columns:repeat(2,1fr); }
  .attempt-top { flex-wrap:wrap; }
}
@media (forced-colors:active) { .unit { border:1px solid ButtonText; } .container-object span { color:CanvasText; text-shadow:none; } .primary { border:2px solid ButtonText; } .error-cross { color:CanvasText; } }

/* Accesso condiviso e messaggi di sincronizzazione. */
.shared-panel { max-width: 72rem; margin: 1.5rem auto; padding: 1.25rem; border: 1px solid #a9c8bf; border-radius: 0.8rem; background: #f5faf7; }
.shared-panel:empty { display: none; }
.shared-heading { display: flex; flex-wrap: wrap; justify-content: space-between; align-items: center; gap: 1rem; }
.shared-panel form, form[data-note] { display: grid; gap: 0.75rem; max-width: 35rem; }
.shared-panel label, form[data-note] label { display: grid; gap: 0.3rem; }
.shared-panel input, form[data-note] textarea { width: 100%; padding: 0.6rem; font: inherit; }
form[data-note] textarea { min-height: 6rem; }
.shared-error { padding: 1rem; margin: 1rem 0; background: #fff3e3; border-left: 0.3rem solid #a65700; }
.attempt-item pre { white-space: pre-wrap; overflow-wrap: anywhere; max-height: 24rem; overflow: auto; }