.ichitasu-b-app{--b1:#91bce5;--b2:#4f8fcb;--b3:#1e5791;max-width:820px;margin:28px auto;color:#252525;font-family:-apple-system,BlinkMacSystemFont,"Hiragino Kaku Gothic ProN","Yu Gothic",YuGothic,Meiryo,sans-serif;line-height:1.85}.ichitasu-b-app *{box-sizing:border-box}.ichitasu-b-app .kicker{font-size:12px;letter-spacing:.14em;color:#777}.ichitasu-b-app h2{margin:0;font-size:clamp(22px,4vw,30px)}.ichitasu-b-app .intro{font-size:14px;color:#5f5f5f;margin:6px 0 20px}.ichitasu-b-app .tabs{display:grid;grid-template-columns:repeat(3,1fr);gap:1px;background:#e5e7eb;border:1px solid #e5e7eb;margin-bottom:22px}.ichitasu-b-app .tab{border:0;background:#fff;padding:12px 8px;cursor:pointer}.ichitasu-b-app .tab strong{display:block}.ichitasu-b-app .tab.active{color:#fff}.ichitasu-b-app .tab[data-level="1"].active{background:var(--b1);color:#17324a}.ichitasu-b-app .tab[data-level="2"].active{background:var(--b2)}.ichitasu-b-app .tab[data-level="3"].active{background:var(--b3)}.ichitasu-b-app .card{border:1px solid #e5e7eb;border-top:4px solid var(--b1);background:#fff}.ichitasu-b-app .card.level-2{border-top-color:var(--b2)}.ichitasu-b-app .card.level-3{border-top-color:var(--b3)}.ichitasu-b-app .head{display:flex;justify-content:space-between;padding:11px 15px;background:#f7faff;border-bottom:1px solid #e5e7eb;font-size:13px}.ichitasu-b-app .body{padding:20px}.ichitasu-b-app .prompt{font-weight:700;margin:0}.ichitasu-b-app .math{text-align:center;font-family:"Times New Roman","Yu Mincho",serif;font-size:1.15rem;margin:8px 0 16px}.ichitasu-b-app .choices{display:grid;gap:8px}.ichitasu-b-app .choice{width:100%;text-align:left;border:1px solid #d4d4d4;background:#fff;padding:10px 12px;cursor:pointer;font-size:15px}.ichitasu-b-app .choice.selected{border-color:#2f6fb0;background:#edf4fb}.ichitasu-b-app .choice.correct{border-color:#2f7657;background:#edf7f1}.ichitasu-b-app .choice.wrong{border-color:#a64b4b;background:#fbefef}.ichitasu-b-app .letter{display:inline-flex;width:24px;height:24px;align-items:center;justify-content:center;border:1px solid #aaa;margin-right:9px;font-size:12px}.ichitasu-b-app .actions{display:flex;flex-wrap:wrap;gap:8px;margin-top:16px}.ichitasu-b-app .btn{border:1px solid #2f6fb0;background:#fff;color:#1f4f82;padding:9px 14px;cursor:pointer;font-weight:700}.ichitasu-b-app .level-1 .primary{background:var(--b1);border-color:var(--b1);color:#17324a}.ichitasu-b-app .level-2 .primary{background:var(--b2);border-color:var(--b2);color:#fff}.ichitasu-b-app .level-3 .primary{background:var(--b3);border-color:var(--b3);color:#fff}.ichitasu-b-app .feedback,.ichitasu-b-app .hint,.ichitasu-b-app .solution{display:none;margin-top:14px}.ichitasu-b-app .feedback.show{display:block;padding:9px 12px;border-left:3px solid}.ichitasu-b-app .feedback.ok{background:#edf7f1;border-color:#2f7657}.ichitasu-b-app .feedback.bad{background:#fbefef;border-color:#a64b4b}.ichitasu-b-app .hint.show{display:block;padding:14px;background:#edf4fb;border-left:3px solid #2f6fb0;font-size:14px}.ichitasu-b-app .solution.show{display:block;border:1px solid #d8d8d8}.ichitasu-b-app .solution-title{padding:10px 14px;background:#eef5fc;border-bottom:1px solid #d8d8d8;font-weight:700}.ichitasu-b-app .paper{padding:18px;background:repeating-linear-gradient(to bottom,#fff 0,#fff 31px,#f1f1f1 32px)}.ichitasu-b-app .step{margin-bottom:15px;background:rgba(255,255,255,.96)}.ichitasu-b-app .sl{font-size:13px;font-weight:700;color:#234f7b}.ichitasu-b-app .st{font-size:14px}.ichitasu-b-app .answer{margin-top:14px;border:2px solid #252525;padding:9px 12px;text-align:center;font-weight:700;background:#fff}.ichitasu-b-app .next{display:flex;justify-content:flex-end;margin-top:16px}@media(max-width:640px){.ichitasu-b-app .tabs{grid-template-columns:1fr}.ichitasu-b-app .body{padding:16px}}