:root{color:#263542;font-synthesis:none;text-rendering:optimizelegibility;-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale;background:#f4f7f7;font-family:Inter,ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,Segoe UI,sans-serif;font-size:16px;line-height:1.5}*{box-sizing:border-box}body{min-width:320px;min-height:100svh;margin:0}h1,h2,h3,p{margin-top:0}h1,h2,h3{color:#17212b;line-height:1.15}h1{margin-bottom:0;font-size:clamp(2rem,7vw,4rem)}h2{margin:0;font-size:clamp(1.35rem,4vw,2rem)}p{margin-bottom:0}.app-shell{width:100%;margin:0 auto;padding:8px}.app-header{flex-direction:column;align-items:flex-start;gap:2px;padding:3px 0 6px;display:flex}.app-header h1{letter-spacing:0;margin:0;font-size:clamp(1.2rem,5.5vw,1.55rem)}.eyebrow{color:#356661;letter-spacing:.08em;text-transform:uppercase;margin:0 0 6px;font-size:.78rem;font-weight:750}.header-copy{color:#4c5967;font-size:.92rem;display:none}.chapter-selector,.mode-tabs,.topic-tabs,.selector-grid{gap:10px;display:grid}.chapter-selector{scrollbar-width:thin;gap:8px;margin:2px -8px 6px;padding:0 8px 4px;display:flex;overflow-x:auto}.chapter-button,.tab,button{color:#1d2730;cursor:pointer;font:inherit;background:#fff;border:1px solid #cfd8dc;border-radius:8px;transition:background .2s,border-color .2s,box-shadow .2s,color .2s}.chapter-button{text-align:left;flex:none;gap:2px;min-width:116px;min-height:48px;padding:8px 10px;display:grid}.chapter-button>span,.practice-topline span{color:#637382;text-transform:uppercase;font-size:.78rem;font-weight:700}.chapter-button strong{color:#17212b;font-size:.92rem;line-height:1.2}.chapter-button small{color:#52606d;font-size:.82rem;display:none}.chapter-full-title{display:none}.chapter-button:hover,.chapter-button.active,.tab:hover,.tab.active,button:hover{border-color:#2f7d73;box-shadow:0 8px 22px #2147501f}.chapter-button.active,.tab.active{background:#e7f4f1}.chapter-summary,.panel,.practice-card,.study-block{background:#fff;border:1px solid #d8e0e4;border-radius:8px}.chapter-summary{flex-direction:column;align-items:flex-start;gap:4px;margin-bottom:6px;padding:6px 8px;display:flex}.chapter-summary h2{margin:0;font-size:.98rem}.chapter-summary span{color:#465663;max-width:420px;font-size:.78rem;line-height:1.35;display:none}.chapter-title-zh{display:none}.mode-tabs{z-index:5;background:#f4f7f7;grid-template-columns:repeat(3,minmax(0,1fr));gap:6px;margin:0 -8px 6px;padding:6px 8px;position:sticky;top:0}.topic-tabs{scrollbar-width:thin;gap:8px;margin:0 -10px 8px;padding:0 10px 4px;display:flex;overflow-x:auto}.selector-grid{grid-template-columns:1fr}.tab{min-height:36px;padding:6px 7px;font-size:.9rem;font-weight:700}.topic-tab,.selector-grid button{text-align:left;flex:none;min-height:38px;padding:7px 10px;font-weight:700}.topic-tab.active{background:#e7f4f1;border-color:#2f7d73}.panel{width:100%;margin:0 auto;padding:10px}.section-heading{margin-bottom:10px}.stack{gap:10px;display:grid}.study-block,.practice-card{padding:10px}.study-block h3,.practice-card h3{color:#17212b;margin:0 0 8px;font-size:1.05rem}.table-wrap{display:none;overflow-x:auto}.vocab-table{border-collapse:collapse;text-align:left;width:100%;min-width:620px}.vocab-table th,.vocab-table td{vertical-align:top;border-bottom:1px solid #e5ecef;padding:8px 10px}.vocab-table th{color:#33414f;font-size:.85rem}.note-list,.memory-list{gap:8px;margin:0;padding-left:22px;font-size:1rem;display:grid}.practice-topline{justify-content:space-between;align-items:center;gap:12px;display:flex}.flashcard{text-align:center;place-items:center;gap:10px;width:100%;min-height:210px;margin:4px 0 10px;padding:18px;display:grid}.flashcard-term{color:#17212b;font-size:clamp(1.75rem,9vw,2.15rem);font-weight:800}.flashcard-zh{color:#2f7d73;font-size:clamp(1.6rem,8vw,2rem);font-weight:700}.button-row{flex-wrap:wrap;gap:10px;display:flex}.button-row button,.answer-form button,.secondary-action,.question-item>button{min-height:42px;padding:8px 13px;font-weight:700}.answer-form{grid-template-columns:minmax(0,1fr);gap:10px;margin-top:10px;display:grid}input{box-sizing:border-box;color:#17212b;width:100%;min-height:50px;font:inherit;border:1px solid #cfd8dc;border-radius:8px;padding:10px 12px;font-size:1.18rem}input:focus,button:focus-visible{outline-offset:2px;outline:3px solid #2f7d7338}.prompt{color:#465663;font-size:1rem}.feedback{border-radius:8px;margin-top:10px;padding:9px 11px;font-size:1.08rem;font-weight:700}.feedback.correct{color:#245b2e;background:#e4f6e8}.feedback.almost{color:#775410;background:#fff5da}.feedback.wrong{color:#8c2f2f;background:#fde8e8}.secondary-action{margin-top:8px}.top-action{margin:0 0 10px}.question-list{gap:12px;display:grid}.question-item{border-top:1px solid #e5ecef;gap:10px;padding-top:12px;display:grid}.question-item:first-child{border-top:0;padding-top:0}.question-item p{color:#263542}.single-question{border-top:0;padding-top:0}.practice-card .single-question>p:first-child,.practice-card .single-question>label{color:#17212b;font-size:clamp(1.25rem,6vw,1.38rem);font-weight:750;line-height:1.25}.meta-list{gap:8px;margin:12px 0 0;display:grid}.meta-list div{grid-template-columns:1fr;gap:2px;display:grid}.meta-list dt{color:#637382;font-weight:700}.meta-list dd{color:#263542;margin:0}.explanation{color:#465663;border-left:3px solid #8fbcb6;padding-left:10px;font-size:1.02rem}.zh-support{color:#33414f}.option-grid{gap:8px;display:grid}.option{text-align:left;min-height:52px;padding:11px 12px;font-size:1.12rem;line-height:1.25}.vocab-card-list{gap:8px;display:grid}.vocab-card{background:#fff;border:1px solid #e0e8eb;border-radius:8px;padding:10px}.vocab-card strong{color:#17212b;margin-bottom:6px;font-size:1.08rem;display:block}.vocab-card dl{gap:4px;margin:0;display:grid}.vocab-card dl div{grid-template-columns:96px minmax(0,1fr);gap:8px;display:grid}.vocab-card dt{color:#637382;font-size:.78rem;font-weight:750}.vocab-card dd{color:#263542;margin:0}.option.selected{background:#e7f4f1;border-color:#2f7d73}@media (width>=700px){.app-shell{width:min(1120px,100%);padding:12px 20px 20px}.app-header{flex-direction:row;justify-content:space-between;align-items:baseline;gap:16px;padding:6px 0 8px}.app-header h1{font-size:clamp(1.35rem,2.4vw,2rem)}.header-copy{display:block}.chapter-selector{grid-template-columns:repeat(3,minmax(0,1fr));margin:4px 0 8px;padding:0;display:grid;overflow:visible}.chapter-button{min-width:0;min-height:62px}.chapter-short-title{display:none}.chapter-full-title,.chapter-button small{display:inline}.chapter-summary{flex-direction:row;justify-content:space-between;align-items:center;gap:12px;padding:8px 10px}.chapter-summary h2{font-size:clamp(1rem,2vw,1.25rem)}.chapter-title-zh,.chapter-summary span{display:inline}.mode-tabs{gap:10px;margin:0 0 8px;padding:0;position:static}.tab{padding:6px 10px;font-size:1rem}.topic-tabs{grid-template-columns:repeat(auto-fit,minmax(180px,1fr));margin:0 0 10px;padding:0;display:grid;overflow:visible}.selector-grid{grid-template-columns:repeat(2,minmax(0,1fr))}.panel{width:min(980px,100%);padding:12px}.study-block,.practice-card{padding:14px}.flashcard{min-height:240px}.flashcard-term{font-size:clamp(2.1rem,5vw,3rem)}.flashcard-zh{font-size:clamp(1.8rem,4vw,2.45rem)}input{font-size:1.3rem}.feedback{font-size:1.2rem}.practice-card .single-question>p:first-child,.practice-card .single-question>label{font-size:clamp(1.35rem,3vw,1.6rem)}.explanation{font-size:1.05rem}.option{font-size:1.28rem}.vocab-card-list{display:none}.table-wrap{display:block}.chapter-summary span{max-width:420px}}@media (width>=980px){.meta-list div{grid-template-columns:120px minmax(0,1fr)}}