.bbuilder-shell{--bb-navy:#0b3f55;--bb-teal:#0b7b88;background:#f5f9f8;color:var(--ink)}
.bbuilder-head{background:linear-gradient(125deg,#0a3b50,#0f6270);color:#fff;padding:34px 0 38px}
.bbuilder-back{display:inline-block;margin-bottom:20px;color:#d9eef1;text-decoration:none;font-weight:760}.bbuilder-back:hover{color:#fff}
.bbuilder-title-row{display:flex;justify-content:space-between;gap:34px;align-items:flex-start}.bbuilder-title-row>div:first-child{max-width:820px}
.bbuilder-head .eyebrow{color:#8fe2e8;margin:0 0 8px}.bbuilder-head h1{margin:0 0 11px;font-size:clamp(2rem,4.4vw,3.55rem);line-height:1.03;letter-spacing:-.045em}.bbuilder-head p{margin:0;max-width:800px;color:#dceff2;font-size:1.02rem}
.bbuilder-board-switch{display:flex;flex:0 0 auto;background:rgba(255,255,255,.1);padding:5px;border:1px solid rgba(255,255,255,.27);border-radius:10px}.bbuilder-board-switch button{border:0;background:transparent;color:#effafb;font-weight:820;padding:9px 14px;border-radius:6px}.bbuilder-board-switch button.is-active{background:#fff;color:var(--bb-navy)}
.bbuilder-tabs{display:grid;grid-template-columns:repeat(5,minmax(0,1fr));background:#fff;border:1px solid var(--line);border-top:0;box-shadow:0 8px 20px rgba(13,58,76,.05)}.bbuilder-tabs button{border:0;border-right:1px solid var(--line);background:#fff;padding:14px 10px;font-weight:800;color:#49606b}.bbuilder-tabs button:last-child{border-right:0}.bbuilder-tabs button span{display:block;font-size:.66rem;letter-spacing:.12em;color:#8a989e}.bbuilder-tabs button.is-active{background:#e8f6f8;color:var(--bb-navy);box-shadow:inset 0 -3px 0 var(--cyan)}
.bbuilder-session-bar{display:flex;align-items:center;margin:25px 0 14px;border-bottom:1px solid var(--line)}.bbuilder-session-bar>div{display:grid;min-width:112px;padding:0 18px 12px;border-right:1px solid var(--line)}.bbuilder-session-bar>div:first-child{padding-left:0}.bbuilder-session-bar small{font-size:.7rem;text-transform:uppercase;letter-spacing:.08em;color:#74838a;font-weight:800}.bbuilder-session-bar strong{color:var(--navy);font-size:1.01rem}.bbuilder-session-bar button{margin-left:auto;margin-bottom:11px;background:transparent;border:1px solid #91a7ad;border-radius:8px;padding:8px 12px;color:var(--navy);font-weight:760}
.bbuilder-workspace{background:#fff;border:1px solid var(--line);padding:clamp(22px,4vw,42px);box-shadow:var(--shadow-soft);min-height:470px}.bbuilder-kicker{margin:0 0 7px;text-transform:uppercase;letter-spacing:.1em;font-weight:850;color:var(--teal2);font-size:.75rem}.bbuilder-question{margin:0 0 8px;color:var(--navy);font-size:clamp(1.65rem,3vw,2.45rem);line-height:1.12}.bbuilder-copy{max-width:850px;margin:0 0 25px;color:var(--muted)}
.bbuilder-ionic-stage{display:grid;grid-template-columns:1fr auto 1fr;gap:18px;align-items:center;max-width:660px;margin:8px auto 30px}.bbuilder-neutral-atom{display:grid;place-items:center;min-height:150px;border:1px solid #bfd1d4;background:#f5faf9}.bbuilder-neutral-atom strong{font-size:3.3rem;color:var(--bb-navy);line-height:1}.bbuilder-neutral-atom span{margin-top:7px;color:#65787f;font-size:.82rem}.bbuilder-transfer-mark{color:#74858b;font-weight:800;text-align:center}
.bbuilder-step-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));border-top:1px solid var(--line);border-left:1px solid var(--line);margin-top:8px}.bbuilder-step-grid fieldset{border:0;border-right:1px solid var(--line);border-bottom:1px solid var(--line);padding:17px 18px;min-width:0}.bbuilder-step-grid legend{float:left;width:100%;margin:0 0 10px;color:#5d7178;font-size:.78rem;text-transform:uppercase;letter-spacing:.055em;font-weight:820}.bbuilder-mini-choices{display:flex;gap:8px;flex-wrap:wrap;clear:both}.bbuilder-mini-choices button{border:1px solid #aebfc4;background:#fff;color:var(--navy);font-weight:800;min-width:52px;padding:10px 12px}.bbuilder-mini-choices button:hover,.bbuilder-mini-choices button.is-selected{background:#eaf7f7;border-color:#0b7181}.bbuilder-mini-choices button.is-selected{box-shadow:inset 0 0 0 1px #0b7181}.bbuilder-mini-choices.is-formula button{font-size:1.04rem}
.bbuilder-statement{border:0;margin:22px 0 0;padding:0}.bbuilder-statement legend{font-weight:850;color:var(--navy);margin-bottom:10px}.bbuilder-statement label{display:flex;gap:11px;align-items:flex-start;padding:12px 13px;border-top:1px solid var(--line);cursor:pointer}.bbuilder-statement label:last-of-type{border-bottom:1px solid var(--line)}.bbuilder-statement label:has(input:checked){background:#eef8f7}.bbuilder-statement input{margin-top:3px;accent-color:#0b7181}.bbuilder-statement span{color:#435a63}
.bbuilder-submit{margin-top:20px;border:0;border-radius:7px;padding:12px 18px;background:var(--teal);color:#fff;font-weight:820}.bbuilder-submit:disabled{opacity:.38;cursor:not-allowed}
.bbuilder-feedback,.bbuilder-explanation{margin-top:14px;padding:18px 20px}.bbuilder-feedback.is-good{background:#edf8ef;border:1px solid #b9dfc1;color:#155b36}.bbuilder-feedback.is-bad{background:#fff2f0;border:1px solid #efc8c1;color:#832f2f}.bbuilder-feedback strong{display:block;font-size:1.04rem}.bbuilder-feedback span{display:block;margin-top:3px}.bbuilder-explanation{background:#f2f6f5;border:1px solid #d5dfdd}.bbuilder-explanation h2{margin:0 0 8px;color:var(--navy);font-size:1.23rem}.bbuilder-explanation p{margin:7px 0;color:#425960}
.bbuilder-ion-reveal{margin-top:18px;padding:18px;border-top:1px solid #cbd8d7;border-bottom:1px solid #cbd8d7;background:#fff}.bbuilder-ion-row{display:flex;justify-content:center;gap:22px;flex-wrap:wrap;padding:18px 0}.bbuilder-ion-card{position:relative;width:104px;height:104px;display:grid;place-items:center}.bbuilder-ion-card strong{font-size:2.25rem;color:var(--bb-navy)}.bbuilder-ion-card sup{position:absolute;right:3px;top:-7px;font-weight:900;color:#173f50;font-size:1rem}.bbuilder-bracket{position:absolute;top:8px;bottom:8px;font-size:5rem;line-height:85px;color:#5b727b;font-weight:300}.bbuilder-bracket.left{left:0}.bbuilder-bracket.right{right:0}.bbuilder-ion-card i{position:absolute;transform:translate(-50%,-50%);font-style:normal;font-weight:900;color:#663c76;font-size:1rem}.bbuilder-electron-key{display:flex;justify-content:center;gap:20px;flex-wrap:wrap;color:#63767d;font-size:.8rem}.bbuilder-electron-key b{font-size:1rem;color:#663c76}.bbuilder-ion-reveal>p{text-align:center;font-size:.74rem;color:#7c898e}.bbuilder-answer-line{display:flex;gap:10px;flex-wrap:wrap;margin-top:15px}.bbuilder-answer-line>span{padding:8px 10px;border:1px solid #d4dedc;background:#fff;color:#596c73;font-size:.82rem}.bbuilder-answer-line strong{color:var(--navy)}
.bbuilder-covalent-layout{display:grid;grid-template-columns:minmax(360px,.92fr) minmax(0,1.08fr);gap:32px;align-items:start}.bbuilder-diagram-panel{border:1px solid #c8d8da;background:#f7fbfa;padding:14px}.bbuilder-diagram-panel header{display:flex;justify-content:space-between;gap:14px;align-items:baseline;padding:2px 4px 8px}.bbuilder-diagram-panel header strong{color:var(--navy)}.bbuilder-diagram-panel header small{color:#74858b}.bbuilder-molecule-svg{display:block;width:100%;height:330px;background:#fff;border-top:1px solid #d8e2e0;border-bottom:1px solid #d8e2e0}.bbuilder-guide{stroke:#c7d3d5;stroke-width:1;stroke-dasharray:3 3}.bbuilder-bond-line{stroke:#526b73;stroke-width:1.4;stroke-linecap:round}.bbuilder-atom{fill:#eef7f7;stroke:#15586c;stroke-width:1.7}.bbuilder-atom-label{fill:#11364a;font-size:5.8px;font-weight:850;text-anchor:middle;dominant-baseline:middle}.bbuilder-bond-electron,.bbuilder-lp-electron{fill:#6d3d76;font-size:4.3px;font-weight:900;text-anchor:middle;dominant-baseline:middle}.bbuilder-build-controls{display:grid;gap:22px}.bbuilder-build-controls section{border-top:1px solid var(--line);padding-top:14px}.bbuilder-build-controls h3{margin:0 0 10px;color:var(--navy);font-size:1rem}.bbuilder-bond-controls{display:grid;gap:8px}.bbuilder-bond-controls button{display:flex;justify-content:space-between;gap:14px;align-items:center;border:1px solid #b6c7ca;background:#fff;padding:11px 13px;color:#50666e;text-align:left}.bbuilder-bond-controls button:hover{background:#eef8f8}.bbuilder-bond-controls strong{color:var(--navy)}.bbuilder-lp-controls{display:grid;border-top:1px solid #d4dedd}.bbuilder-lp-controls>div{display:grid;grid-template-columns:minmax(120px,1fr) 38px 38px 38px;gap:6px;align-items:center;padding:8px 0;border-bottom:1px solid #d4dedd}.bbuilder-lp-controls span{color:#526870}.bbuilder-lp-controls button{height:34px;border:1px solid #b7c6c9;background:#fff;color:var(--navy);font-size:1.1rem;font-weight:800}.bbuilder-lp-controls strong{text-align:center;color:var(--navy)}.bbuilder-correct-diagram{max-width:560px;margin:16px auto;background:#fff;border:1px solid #d2dedd}.bbuilder-board-tip{padding:11px 13px;background:#edf7f7;border-left:3px solid var(--teal);font-size:.85rem}
.bbuilder-dative-stage{display:grid;grid-template-columns:1fr auto 1fr;gap:16px;align-items:center;max-width:720px;margin:20px auto 28px}.bbuilder-dative-stage>button{border:1px solid #aebfc4;background:#f7fbfa;min-height:145px;padding:20px;color:var(--navy)}.bbuilder-dative-stage>button strong{display:block;font-size:2.1rem}.bbuilder-dative-stage>button span{display:block;margin-top:8px;color:#72848b;font-size:.8rem}.bbuilder-dative-stage>button:hover,.bbuilder-dative-stage>button.is-selected{border-color:#0b7181;background:#eaf7f7}.bbuilder-dative-stage>b{color:#7e8d92;font-size:1.5rem}.bbuilder-step-grid.is-dative{grid-template-columns:repeat(3,minmax(0,1fr))}.bbuilder-arrow-field{grid-column:auto}.bbuilder-dative-reveal{position:relative;display:grid;place-items:center;gap:6px;max-width:420px;margin:16px auto;padding:22px;border-top:1px solid #cbd8d7;border-bottom:1px solid #cbd8d7;background:#fff}.bbuilder-dative-reveal strong{font-size:2rem;color:var(--bb-navy)}.bbuilder-dative-reveal span:last-child{font-size:.78rem;color:#718087}.bbuilder-donor-pair{position:absolute;left:18px;top:13px;color:#6d3d76;font-weight:900;letter-spacing:2px}
.bbuilder-board-note{margin-top:18px;padding:15px 18px;border-left:4px solid var(--teal);background:#eef7f7;color:#38535b}.bbuilder-board-note strong{color:var(--navy)}.bbuilder-rule-strip{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));margin-top:26px;border-top:1px solid #c8d7d5;border-left:1px solid #c8d7d5}.bbuilder-rule-strip article{padding:15px 17px;border-right:1px solid #c8d7d5;border-bottom:1px solid #c8d7d5;background:#fff}.bbuilder-rule-strip strong{display:block;color:var(--navy)}.bbuilder-rule-strip span{display:block;margin-top:4px;color:#667a81;font-size:.82rem;line-height:1.4}.bbuilder-foot{display:flex;justify-content:space-between;gap:20px;color:#7b898e;font-size:.78rem;padding:20px 2px 0}.bbuilder-foot a{color:#59737c}
@media(max-width:900px){.bbuilder-title-row{display:grid}.bbuilder-board-switch{justify-self:start}.bbuilder-tabs{grid-template-columns:repeat(3,1fr)}.bbuilder-tabs button:nth-child(3){border-right:0}.bbuilder-tabs button:nth-child(-n+3){border-bottom:1px solid var(--line)}.bbuilder-covalent-layout{grid-template-columns:1fr}.bbuilder-diagram-panel{order:-1}.bbuilder-step-grid.is-dative{grid-template-columns:1fr 1fr}.bbuilder-arrow-field{grid-column:1/-1}.bbuilder-rule-strip{grid-template-columns:1fr}.bbuilder-representation{display:none}}
@media(max-width:620px){.bbuilder-head{padding-top:24px}.bbuilder-tabs{grid-template-columns:repeat(2,1fr)}.bbuilder-tabs button{border-bottom:1px solid var(--line)}.bbuilder-tabs button:nth-child(2n){border-right:0}.bbuilder-tabs button:last-child{grid-column:1/-1;border-bottom:0}.bbuilder-session-bar{flex-wrap:wrap;gap:8px;border-bottom:0}.bbuilder-session-bar>div{border:1px solid var(--line);padding:8px 10px;min-width:83px}.bbuilder-session-bar>div:first-child{padding-left:10px}.bbuilder-session-bar button{margin:0 0 0 auto}.bbuilder-workspace{padding:20px 15px;min-height:420px}.bbuilder-step-grid,.bbuilder-step-grid.is-dative{grid-template-columns:1fr}.bbuilder-arrow-field{grid-column:auto}.bbuilder-ionic-stage,.bbuilder-dative-stage{grid-template-columns:1fr}.bbuilder-transfer-mark{transform:rotate(90deg);min-height:20px}.bbuilder-dative-stage>b{display:grid;place-items:center}.bbuilder-molecule-svg{height:280px}.bbuilder-diagram-panel header{display:grid}.bbuilder-foot{display:grid}.bbuilder-lp-controls>div{grid-template-columns:minmax(90px,1fr) 36px 36px 36px}}
.bbuilder-donor-pair.is-right{left:auto;right:18px}