:root{--ink:#142b40;--muted:#607588;--bg:#f3f6f8;--paper:#fff;--line:#dce5eb;--blue:#2775ae;--bluep:#e9f3fb;--teal:#257963;--tealp:#e8f4f0;--amber:#bb7540;--amberp:#fff2e5;--shadow:0 9px 38px rgba(16,39,59,.07)}
*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;background:var(--bg);color:var(--ink);font:16px/1.6 -apple-system,BlinkMacSystemFont,'Segoe UI',Arial,sans-serif}button,input,select{font:inherit}button{cursor:pointer}a{color:var(--blue)}:focus-visible{outline:3px solid #367fae;outline-offset:3px}
.exam-head{position:sticky;top:0;z-index:80;background:#fffe;border-bottom:1px solid #d6e4ed;padding:8px clamp(14px,3vw,35px);display:flex;gap:12px;align-items:center;box-shadow:0 3px 14px #1839500e;min-height:60px}.home-link{display:inline-flex;align-items:center;justify-content:center;text-decoration:none;color:#fff;background:#154e72;border-radius:10px;padding:9px 13px;white-space:nowrap;min-height:44px;font-weight:800;font-size:13px}.exam-head strong{font-size:14px;line-height:1.3}.exam-head span{color:var(--muted);font-size:12px;margin-left:auto}
.exam-main{max-width:1080px;margin:0 auto;padding:28px clamp(14px,3vw,40px) 100px}.hero{background:linear-gradient(120deg,#112c43,#205e7e 72%,#237469);color:#fff;border-radius:19px;padding:37px clamp(22px,5vw,45px);position:relative;overflow:hidden}.hero:before{content:'F = ma';position:absolute;right:-24px;top:-12px;font-size:88px;transform:rotate(-14deg);color:#ffffff0d;font-weight:900;pointer-events:none}.hero small{letter-spacing:.14em;color:#bce8e7;font-weight:850;font-size:11px}.hero h1{margin:9px 0;font-size:clamp(28px,4.7vw,48px);letter-spacing:-.035em;line-height:1.1}.hero p{max-width:720px;color:#d9ebf6;line-height:1.55;font-size:15px;margin:12px 0 0}
.info-rail{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:14px;margin:16px 0 25px}.stat{padding:15px 17px;border:1px solid var(--line);border-radius:13px;background:#fff;display:grid;gap:2px}.stat b{font-size:21px}.stat span{font-size:12px;color:var(--muted)}
.panel{border:1px solid var(--line);border-radius:18px;background:var(--paper);box-shadow:var(--shadow);padding:clamp(19px,3vw,33px);margin:23px 0}.panel-head{border-bottom:1px solid var(--line);padding-bottom:18px;margin-bottom:19px}.panel-head small{color:var(--teal);font-size:11px;letter-spacing:.12em;font-weight:800}.panel h2{margin:4px 0 8px;font-size:clamp(22px,2.8vw,29px);line-height:1.25}.panel-head p{font-size:14px;color:var(--muted);margin:0}
.breadcrumbs{display:flex;flex-wrap:wrap;gap:8px;margin:12px 0}.tiny-link{border-radius:999px;text-decoration:none;background:var(--bluep);color:#235d7e;padding:6px 12px;font-weight:750;font-size:12px}
.concept-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:14px}.concept{background:#f5f9fc;border:1px solid #d5e4eb;padding:17px;border-radius:14px;min-width:0}.concept h3{margin:0;font-size:15px}.concept p{font-size:13px;color:#415a6d;margin:9px 0 0;line-height:1.5}.concept .formula{font-size:19px;color:#1b668f;font-weight:850;margin:10px 0}.concept .diagram{padding:3px;margin-top:9px;min-height:132px}.concept svg{display:block;width:100%;height:auto}
.choice-controls{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:13px;margin:19px 0}.choice-controls label{font-size:12px;font-weight:750;color:#37546a}.choice-controls select{display:block;margin-top:6px;width:100%;background:white;border:1px solid #b9cfde;border-radius:10px;min-height:46px;padding:9px 10px;color:var(--ink)}
.mode-tabs{display:flex;gap:8px;flex-wrap:wrap}.mode-tabs button{border:1px solid #bdd1dc;background:white;color:#345570;border-radius:10px;padding:9px 17px;font-weight:800;min-height:44px}.mode-tabs button[aria-pressed=true]{background:#1c668f;border-color:#1c668f;color:white}.btn{border:1px solid #bed2df;background:white;color:#1d5275;border-radius:10px;padding:10px 17px;font-weight:800;min-height:44px}.btn:hover{background:#eaf5fb}.btn.primary{color:white;background:#1c668f;border-color:#1c668f}.btn.primary:hover{background:#124a6c}.btn:disabled{opacity:.45;cursor:not-allowed}.toolbar{display:flex;gap:9px;align-items:center;flex-wrap:wrap;margin:20px 0}.subtle{color:var(--muted);font-size:13px}.hidden{display:none!important}.topic-badges{display:flex;align-items:center;gap:8px;flex-wrap:wrap}.tier{border-radius:7px;font-size:11px;font-weight:900;letter-spacing:.07em;background:#e7f3ec;color:#1f755b;padding:5px 9px}.tier.t2{background:#e7f0fa;color:#245c97}.tier.i{background:#fcece3;color:#96582e}.tier.r{background:#edf1f4;color:#445970}
.sheet{border-top:1px solid var(--line);padding-top:21px}.question{border:1px solid #ccdfe9;border-radius:16px;background:#fff;padding:clamp(18px,3vw,26px);margin:18px 0 23px;scroll-margin-top:76px}.question h3{font-size:19px;margin:14px 0 14px;line-height:1.5;font-weight:760}.q-top{display:flex;justify-content:space-between;align-items:center;gap:11px;flex-wrap:wrap}.q-number{font-size:12px;color:var(--muted);font-weight:800}.q-unit{color:var(--muted);font-weight:800}.question .diagram{margin:15px 0 17px;padding:15px;background:#f5f9fc;border:1px solid #dbe7ed;border-radius:14px;overflow:hidden}.diagram-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:12px}.diagram-part{min-width:0}.diagram-part small{display:block;text-align:center;font-size:12px;font-weight:800;color:#315e77}.diagram svg{display:block;width:100%;height:auto}.diagram-caption{font-size:12px;color:#567084;margin-top:6px;text-align:center}.diagram-single{max-width:670px;margin:0 auto}.choice-options{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:10px}.option{display:flex;align-items:center;gap:12px;background:#f6f9fb;border:1px solid #d8e4eb;border-radius:10px;padding:11px 12px;font-size:14px;cursor:pointer;min-height:48px}.option:has(input:checked){border-color:#2277a8;background:#e9f5fc}.option input{accent-color:#2679a9;min-width:17px;min-height:17px;margin:0}.response{display:flex;gap:10px;align-items:center;flex-wrap:wrap}.response input{max-width:260px;width:100%;font-size:20px;border:1px solid #b7cfdd;border-radius:10px;min-height:52px;padding:10px 14px}.feedback{border-radius:12px;padding:13px 16px;margin:13px 0;font-size:14px;line-height:1.6}.feedback.good{background:#e5f5eb;border:1px solid #a6dac2;color:#16553b}.feedback.bad{background:#fff0e7;border:1px solid #ebc7ac;color:#7c472a}.working{border:1px solid #c5dbe7;border-radius:14px;overflow:hidden;margin:15px 0 0}.working summary{cursor:pointer;font-size:14px;font-weight:850;padding:13px 16px;background:#e9f4fa;color:#1c6286}.working[open] summary{border-bottom:1px solid #c5dbe7}.steps{display:grid;gap:0;padding:8px 16px 12px}.calc-step{display:grid;grid-template-columns:142px minmax(0,1fr);gap:16px;padding:11px 0;border-bottom:1px dashed #d6e4eb}.calc-step:last-child{border-bottom:0;background:#e9f6ed;border-radius:8px;margin:6px -7px;padding:11px 7px}.calc-step strong{font-size:11px;color:#20785e;letter-spacing:.065em;line-height:1.5}.calc-step span{font-size:15px;white-space:pre-line;overflow-wrap:anywhere;line-height:1.65}
.result{padding:24px;background:#f5f9fc;border:1px solid #c6dce8;border-radius:15px;scroll-margin-top:80px}.result h2{margin:0 0 10px}.result .score{font-size:34px;font-weight:850;color:#1c618b}.diagnostic{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:10px;margin:15px 0}.diag-stat{border-radius:10px;padding:14px;background:white;border:1px solid #d4e3ec}.diag-stat strong{font-size:22px;display:block}.diag-stat small{font-size:12px;color:#4e6a7f}.report-rows{display:grid;gap:5px;font-size:13px}.report-rows span{background:white;padding:8px 11px;border-radius:6px}.foot{color:#607588;font-size:12px;border-top:1px solid var(--line);margin-top:40px;padding-top:18px}.progress-track{height:9px;background:#e3edf2;border-radius:99px;overflow:hidden;flex:1;max-width:350px}.progress-fill{height:100%;background:#2c9075;width:0;transition:width .2s}.blank{border:1px dashed #b4cbd9;border-radius:13px;background:#f8fbfd;padding:21px;color:#526c7e}
@media(max-width:900px){.concept-grid{grid-template-columns:1fr 1fr}.choice-controls{grid-template-columns:repeat(2,minmax(0,1fr))}.diagram-grid{grid-template-columns:1fr}}
@media(max-width:600px){.exam-head span{display:none}.exam-head strong{font-size:12px}.info-rail{grid-template-columns:1fr 1fr}.concept-grid,.choice-controls,.choice-options,.diagnostic{grid-template-columns:1fr}.exam-main{padding:16px 12px 70px}.question{padding:17px}.calc-step{grid-template-columns:1fr;gap:2px}.hero{padding:28px 20px}.panel{padding:20px}.concept-grid{gap:12px}}
@media print{.exam-head,.choice-controls,.mode-tabs,.toolbar,.btn,.foot{display:none!important}.question,.panel{break-inside:avoid;box-shadow:none}.hero{-webkit-print-color-adjust:exact;print-color-adjust:exact}}

/* V2 visual style: boxed formulas and large annotated diagrams */
.concept .formula{background:#112d45;color:#f7fbff;padding:11px 12px;border-radius:11px;line-height:1.55;font-weight:700;font-size:clamp(16px,1.6vw,19px);overflow-wrap:break-word}.concept .formula sub{font-size:.7em}.concept-art{width:100%;max-height:130px;padding:7px 5px 0}.concept-art svg{display:block;width:100%;height:auto;max-height:105px}.concept-art svg text{font:14px Arial,sans-serif;fill:#284a63}

.exam-print-buttons{display:flex;align-items:center;flex-wrap:wrap;gap:9px;margin:12px 0 20px;padding:11px 14px;background:#edf6f8;border:1px solid #cddfe7;border-radius:12px;font:700 13px/1.4 -apple-system,BlinkMacSystemFont,Arial,sans-serif}
.exam-print-buttons button{border:1px solid #91b9c6;border-radius:9px;padding:10px 13px;background:#fff;color:#1b5877;font:inherit;min-height:44px;cursor:pointer}
.exam-print-buttons span{font-size:12px;color:#567184;flex:1}
@media print{.exam-print-buttons{display:none!important}}

.mistake-reason{display:flex;align-items:center;gap:10px;flex-wrap:wrap;font-weight:750;margin:10px 0 1px;font-size:13px}.mistake-reason select{border:1px solid #a9c5d3;border-radius:8px;padding:8px;background:#fff;max-width:100%;min-height:44px;color:#22495e}.practice-suggestion{margin:18px 0;padding:15px 17px;background:#eff7f6;border:1px solid #b7d8ce;border-radius:10px}.practice-suggestion p{margin:7px 0 11px}
@media print{.mistake-reason,.practice-suggestion{display:none!important}}