:root{color-scheme:light;--background:#f5f7fa;--surface:#fff;--ink:#1d2738;--muted:#77839a;--blue:#3565dc;--blue-hover:#2855c4;--blue-pale:#edf3ff;--border:#e1e6ef;--radius:18px;--sidebar-width:246px;--shadow:0 6px 22px #23365308;font-family:-apple-system,BlinkMacSystemFont,"Hiragino Kaku Gothic ProN","Noto Sans JP","Yu Gothic",Meiryo,sans-serif;font-synthesis:none}
*{box-sizing:border-box}body{margin:0;background:var(--background);color:var(--ink);font-size:15px;line-height:1.7}button,select,input{font:inherit}button,select{color:inherit}button,a,input,select,summary{-webkit-tap-highlight-color:transparent}button,a,select,input[type=checkbox],summary{touch-action:manipulation}button{cursor:pointer}button:disabled{cursor:default}a{color:var(--blue)}button:focus-visible,a:focus-visible,input:focus-visible,select:focus-visible,summary:focus-visible{outline:3px solid #85a9ff;outline-offset:4px}button{transition:background .16s,border-color .16s,transform .16s}button:active:not(:disabled){transform:translateY(1px)}.sr-only{position:absolute;width:1px;height:1px;padding:0;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}.skip-link{position:fixed;left:12px;top:-70px;z-index:30;padding:10px 18px;border-radius:8px;background:var(--surface);box-shadow:var(--shadow)}.skip-link:focus{top:12px}
.sidebar{position:fixed;inset:0 auto 0 0;width:var(--sidebar-width);display:flex;flex-direction:column;background:var(--surface);border-right:1px solid var(--border);padding:24px 15px 20px;z-index:10}.brand{display:inline-flex;flex-direction:column;align-self:flex-start;text-decoration:none;margin:0 14px 35px;color:#101725;line-height:1}.brand-name{font-weight:850;font-size:49px;letter-spacing:-1.8px}.brand-subtitle{font-size:9px;letter-spacing:5.3px;font-weight:650;padding:8px 0 0 3px;color:#354c75}.sidebar-heading{display:flex;align-items:center;justify-content:space-between;font-size:13px;margin:0 14px 11px;font-weight:600}.sidebar-heading>span:last-child{font-weight:400;color:var(--muted);font-variant-numeric:tabular-nums}.section-nav{overflow-y:auto;scrollbar-width:thin;scrollbar-color:#d7deea transparent;flex:1;padding-right:2px}.section-button{position:relative;width:100%;border:0;background:transparent;border-radius:8px;min-height:46px;display:flex;align-items:center;justify-content:space-between;text-align:left;padding:10px 18px 10px 26px;margin-bottom:2px;font-size:14px;line-height:1.4}.section-button:hover{background:#f6f8fb}.section-button[aria-current=true]{color:var(--blue);background:var(--blue-pale);font-weight:600}.section-button[aria-current=true]:before{position:absolute;content:"";left:0;top:7px;bottom:7px;width:4px;border-radius:4px;background:var(--blue)}.section-button .nav-progress{font-size:12px;font-weight:400;color:var(--muted);font-variant-numeric:tabular-nums}.section-button.completed .nav-progress{color:#39745e}.sidebar-note{font-size:11px;color:var(--muted);margin:22px 14px 0;white-space:nowrap}
.workspace{margin-left:var(--sidebar-width);min-height:100dvh;padding:60px 52px 32px;outline:none}.study-container{max-width:1030px;margin:0 auto}.study-heading{display:flex;align-items:center;justify-content:space-between;gap:24px;margin-bottom:13px}.study-heading h1{font-size:32px;letter-spacing:-.7px;line-height:1.25;margin:0 0 2px;font-weight:750;color:#111b2c}.study-heading p{margin:0;color:var(--muted);font-size:17px;letter-spacing:.02em}.study-options{display:flex;gap:22px;flex-wrap:wrap;font-size:13px;font-weight:550;align-items:center}.study-options label{display:flex;align-items:center;gap:8px;cursor:pointer;white-space:nowrap}.study-options input{width:17px;height:17px;margin:0;accent-color:var(--blue);cursor:pointer}.section-progress{display:flex;gap:12px;align-items:center;margin-bottom:26px}.section-progress progress{width:100%;height:7px;border:0;appearance:none;border-radius:8px;overflow:hidden;background:#e3e9f2}.section-progress progress::-webkit-progress-bar{background:#e3e9f2;border-radius:8px}.section-progress progress::-webkit-progress-value{background:var(--blue);border-radius:8px;transition:width .25s}.section-progress progress::-moz-progress-bar{background:var(--blue);border-radius:8px}.section-progress>span{font-size:13px;color:var(--muted);white-space:nowrap;min-width:39px;text-align:right;font-variant-numeric:tabular-nums}
.flashcard{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);box-shadow:var(--shadow);padding:22px 24px 27px;animation:arrive .22s ease-out}.card-meta{display:flex;justify-content:space-between;align-items:center;margin-bottom:18px;font-size:13px;line-height:1.4;font-variant-numeric:tabular-nums}.card-meta-right{display:flex;gap:14px;align-items:center;color:var(--muted)}.image-toggle{border:0;background:transparent;color:var(--muted);padding:0;font-size:11px;text-decoration:underline;text-underline-offset:3px}.image-toggle:hover{color:var(--blue)}.scene-frame{height:clamp(220px,33vh,360px);border-radius:9px;overflow:hidden;margin:0;display:flex;align-items:center;justify-content:center;background:#fafbfc}.scene-image{display:block;object-fit:contain;max-width:100%;max-height:100%;width:100%;height:100%}.scene-unavailable{color:var(--muted);font-size:13px;display:flex;align-items:center;justify-content:center;min-height:180px;background:#f6f8fb;border-radius:9px}.prompt-area{padding:32px 20px 0;text-align:center}.japanese-prompt{font-size:clamp(20px,1.8vw,28px);font-weight:650;line-height:1.7;letter-spacing:.01em;margin:0 auto;max-width:840px;text-wrap:pretty}.prompt-hint{font-size:14px;color:var(--muted);margin:15px 0 26px;line-height:1.7}.button{border:1px solid var(--border);border-radius:9px;background:var(--surface);padding:12px 24px;min-height:48px;font-weight:600;line-height:1.4}.button-primary{border-color:var(--blue);background:var(--blue);color:white}.button-primary:hover{background:var(--blue-hover);border-color:var(--blue-hover)}.reveal-button{width:min(100%,440px);display:inline-flex;align-items:center;justify-content:center;gap:16px;font-size:17px;min-height:52px}.reveal-button kbd{color:#eef4ff;border-color:#ffffff60;background:#ffffff0b;font-size:11px;line-height:1.6}.card-navigation{display:flex;justify-content:space-between;align-items:center;gap:12px;margin-top:18px}.button-nav{display:flex;align-items:center;justify-content:center;gap:12px;min-height:46px;font-size:13px;color:var(--blue);border-color:#cfdbf5;padding:10px 18px}.button-nav>span{font-size:27px;font-weight:350;line-height:.6}.button-nav:hover:not(:disabled){background:var(--blue-pale);border-color:#adc4f1}.button-nav:disabled{color:#a4adbd;border-color:#dce2ec;background:transparent;opacity:.8}.direction-label{color:var(--muted);font-size:12px}.direction-label>span{margin:0 6px}.keyboard-hint{color:#8490a4;font-size:10px;margin:18px 0 0;text-align:center;display:flex;justify-content:center;align-items:center;flex-wrap:wrap;gap:19px}.keyboard-hint>span{display:inline-flex;align-items:center;gap:6px}kbd{border:1px solid #cbd3e0;border-radius:4px;font:inherit;padding:0 5px;background:#ffffff69;line-height:1.7}.section-message{text-align:center;color:#39745e;font-size:13px;margin:16px 0 0}.mobile-bar{display:none}
.answer-heading{font-size:clamp(25px,2.6vw,37px);font-weight:680;line-height:1.5;letter-spacing:-.025em;margin:22px 0 13px;overflow-wrap:anywhere;text-wrap:pretty}.answer-translation{font-size:17px;color:var(--muted);line-height:1.8;margin:0 0 23px}.audio-section{border-top:1px solid var(--border);padding-top:18px;margin-bottom:18px}.audio-controls{display:flex;justify-content:space-between;align-items:center;gap:15px}.audio-play{display:flex;align-items:center;gap:10px;border-color:#83a3f0;color:var(--blue);font-size:14px;min-height:44px;padding:10px 20px}.audio-play:hover{background:var(--blue-pale)}.audio-icon{width:13px;height:13px;fill:currentColor;flex-shrink:0}.speed-control{display:flex;align-items:center;gap:9px;color:var(--muted);font-size:11px;white-space:nowrap}.speed-control select{border:1px solid #cbd3e0;border-radius:7px;background:var(--surface);padding:7px 25px 7px 9px;min-height:38px;font-size:13px}.audio-timeline{display:flex;align-items:center;gap:10px;padding-top:11px}.audio-timeline input{width:100%;height:3px;accent-color:var(--blue);cursor:pointer}.audio-time{font-size:10px;color:var(--muted);font-variant-numeric:tabular-nums;min-width:72px;text-align:right;white-space:nowrap}.audio-error{font-size:12px;color:#9f4935;margin:10px 0 0}.ipa-block{background:#f1f5fa;border-radius:10px;padding:13px 19px;margin:0 0 14px}.ipa-label{font-size:12px;color:var(--muted);margin:0 0 3px}.ipa-content{font-family:"Charis SIL","Doulos SIL","DejaVu Sans",Arial,sans-serif;font-size:20px;line-height:1.8;overflow-wrap:anywhere}.ipa-content p{margin:0 0 5px}.ipa-content p:last-child{margin-bottom:0}.ipa-content strong{font-weight:600}.explanation{border:1px solid #dce5f3;border-radius:9px;overflow:hidden;margin-top:10px}.explanation summary{list-style:none;position:relative;font-weight:650;font-size:14px;padding:13px 42px 13px 19px;cursor:pointer;background:#f7f9fc}.explanation summary::-webkit-details-marker{display:none}.explanation summary:after{content:"";position:absolute;right:20px;top:18px;width:8px;height:8px;border-right:1.8px solid currentColor;border-bottom:1.8px solid currentColor;transform:rotate(45deg);transition:transform .18s}.explanation[open] summary{color:var(--blue);border-bottom:1px solid #edf0f6}.explanation[open] summary:after{transform:rotate(225deg);top:22px}.explanation-body{padding:14px 19px 16px;font-size:14px;line-height:1.95;overflow-wrap:anywhere}.markdown>:first-child{margin-top:0}.markdown>:last-child{margin-bottom:0}.markdown p{margin:0 0 12px}.markdown h2,.markdown h3,.markdown h4{font-size:15px;line-height:1.7;font-weight:650;margin:18px 0 9px}.markdown h2{font-size:17px}.markdown ul,.markdown ol{padding-left:23px;margin:9px 0 13px}.markdown li{margin:4px 0}.markdown blockquote{margin:12px 0;padding:1px 0 1px 15px;border-left:3px solid #d7e1f3;color:#637189}.markdown code{background:#f0f3f8;border-radius:4px;padding:2px 5px;font-family:ui-monospace,SFMono-Regular,Menlo,monospace;font-size:.87em}.markdown pre{background:#f3f6fa;padding:12px;overflow-x:auto;border-radius:6px}.markdown pre code{background:none;padding:0}.markdown strong{font-weight:650}.markdown a{text-underline-offset:3px}.markdown hr{border:0;border-top:1px solid var(--border);margin:18px 0}.markdown .table-wrap{overflow-x:auto;margin:12px 0}.markdown table{border-collapse:collapse;width:100%;font-size:12px}.markdown th,.markdown td{border:1px solid var(--border);padding:6px 10px;text-align:left;vertical-align:top}.markdown th{background:#f4f7fc;font-weight:600}.grading-actions{display:grid;grid-template-columns:1fr 1fr;gap:15px;margin-top:19px}.grading-actions .button{font-size:16px;min-height:50px}.button-again{border-color:#b8c5dc;background:#fafbfd;color:#586980}.button-again:hover{background:#f0f4fa}.grading-actions .button[aria-pressed=true]{box-shadow:0 0 0 3px #d8e5ff}.button-again[aria-pressed=true]{background:#edf2fa;border-color:#6b86b3;box-shadow:0 0 0 3px #e1e8f4}.back-to-prompt{display:block;margin:12px auto -7px;background:none;border:0;color:var(--muted);font-size:12px;padding:5px 12px}.back-to-prompt:hover{color:var(--blue)}.grade-feedback{font-size:12px;color:#657796;margin:10px 0 0;text-align:center}.empty-card{text-align:center;padding:70px 32px}.empty-card h2{font-size:23px;line-height:1.6;margin:0 0 14px}.empty-card p{color:var(--muted);font-size:14px;line-height:1.9;margin:0 auto 24px;max-width:450px}.loading-card{min-height:510px;display:flex;flex-direction:column;align-items:center;justify-content:center;color:var(--muted);font-size:14px}.loading-mark{width:28px;height:28px;border:2px solid #dce5f5;border-top-color:var(--blue);border-radius:50%;animation:spin .8s linear infinite;margin-bottom:20px}@keyframes spin{to{transform:rotate(360deg)}}@keyframes arrive{from{opacity:.6;transform:translateY(3px)}to{opacity:1;transform:translateY(0)}}
@media(min-width:1600px){.workspace{padding-top:72px}.scene-frame{height:360px}}
@media(max-width:1150px){:root{--sidebar-width:215px}.workspace{padding:38px 30px 28px}.sidebar{padding-left:12px;padding-right:12px}.study-heading h1{font-size:29px}.study-heading p{font-size:15px}.study-options{gap:13px;font-size:11px}.scene-frame{height:285px}.japanese-prompt{font-size:23px}.prompt-area{padding:27px 9px 0}.prompt-hint{font-size:12px}.keyboard-hint{gap:12px}.keyboard-hint>span:last-child{display:none}}
@media(max-width:800px){:root{--sidebar-width:185px}.workspace{padding:32px 22px}.sidebar{padding-left:9px;padding-right:9px}.brand-name{font-size:44px}.brand-subtitle{font-size:8px;letter-spacing:4.6px}.section-button{padding-left:19px;padding-right:12px;font-size:12px;min-height:43px}.section-button .nav-progress{font-size:10px}.sidebar-heading{font-size:11px;margin-left:11px;margin-right:11px}.sidebar-note{font-size:9px;margin-left:11px}.study-heading{align-items:flex-start;flex-direction:column;gap:13px}.study-options{gap:21px}.study-heading h1{font-size:28px}.section-progress{margin-bottom:20px}.flashcard{padding:18px 20px 23px}.scene-frame{height:260px}.japanese-prompt{font-size:21px}.prompt-area{padding:25px 0 0}.button-nav{font-size:11px;padding:10px 13px;gap:8px}.direction-label{font-size:10px}.answer-heading{font-size:27px}.answer-translation{font-size:15px}.ipa-content{font-size:18px}.keyboard-hint{font-size:9px}}
@media(max-width:600px){.sidebar{display:none}.workspace{margin:0;padding:0 17px 23px}.mobile-bar{display:flex;align-items:center;justify-content:space-between;margin:0 -17px 23px;padding:14px 20px;background:var(--surface);border-bottom:1px solid var(--border);min-height:68px}.mobile-brand{font-size:29px;font-weight:850;line-height:1;letter-spacing:-1px}.mobile-bar select{appearance:auto;max-width:65%;font-size:12px;border:1px solid var(--border);background:var(--surface);border-radius:7px;padding:7px 9px;min-height:36px}.study-heading{gap:15px;margin-bottom:12px}.study-heading h1{font-size:27px;line-height:1.25}.study-heading p{font-size:13px;margin-top:3px}.study-options{gap:24px;font-size:11px}.study-options input{width:16px;height:16px}.section-progress{margin-bottom:18px}.section-progress progress{height:6px}.section-progress>span{font-size:11px}.flashcard{padding:16px 16px 22px;border-radius:14px;box-shadow:0 4px 15px #23365305}.card-meta{font-size:11px;margin-bottom:14px}.image-toggle{font-size:10px}.card-meta-right{gap:10px}.scene-frame{height:auto;aspect-ratio:4/3;background:#fafbfc;border-radius:7px;max-height:300px}.japanese-prompt{font-size:20px;line-height:1.8;font-weight:650}.prompt-area{padding:23px 0 0}.prompt-hint{font-size:11px;margin:12px 0 21px}.reveal-button{font-size:15px;min-height:49px;width:100%}.reveal-button kbd{display:none}.card-navigation{margin-top:15px;gap:8px}.button-nav{font-size:11px;padding:10px 12px;min-height:43px;gap:7px}.button-nav>span{font-size:24px}.direction-label{font-size:9px;white-space:nowrap}.direction-label>span{margin:0 3px}.keyboard-hint{display:none}.answer-heading{font-size:25px;line-height:1.5;letter-spacing:-.02em;margin:21px 0 12px}.answer-translation{font-size:14px;line-height:1.8;margin-bottom:20px}.audio-section{padding-top:16px;margin-bottom:16px}.audio-play{font-size:12px;padding:10px 13px;min-height:42px;gap:8px}.speed-control{font-size:10px;gap:6px}.speed-control select{font-size:12px;min-height:36px;padding-right:18px}.audio-timeline{padding-top:10px}.audio-time{font-size:9px;min-width:66px}.ipa-block{padding:12px 14px;border-radius:8px}.ipa-label{font-size:11px}.ipa-content{font-size:17px;line-height:1.75}.explanation summary{font-size:13px;padding:12px 35px 12px 14px}.explanation summary:after{right:15px;top:17px;width:7px;height:7px}.explanation[open] summary:after{top:21px}.explanation-body{font-size:13px;padding:13px 14px;line-height:1.95}.markdown h2{font-size:15px}.markdown h3,.markdown h4{font-size:14px}.grading-actions{gap:10px;margin-top:17px}.grading-actions .button{font-size:14px;min-height:47px;padding:10px}.back-to-prompt{font-size:11px;margin-top:11px}.grade-feedback{font-size:11px}.empty-card{padding:50px 20px}.empty-card h2{font-size:20px}.empty-card p{font-size:13px}.section-message{font-size:12px}}
@media(prefers-reduced-motion:reduce){*,*:before,*:after{animation:none!important;transition:none!important;scroll-behavior:auto!important}}
@media(max-width:360px){.card-navigation .direction-label{display:none}.card-navigation .button-nav{flex:1}.audio-controls{gap:8px}.audio-play{padding-left:10px;padding-right:10px}.speed-control{gap:4px}}
.sentence-control{display:flex;align-items:center;gap:12px;margin-bottom:13px;font-size:11px;color:var(--muted)}.sentence-control>span{flex-shrink:0}.sentence-control select{font-size:12px;min-width:0;max-width:100%;flex:1;border:1px solid var(--border);border-radius:7px;background:var(--surface);padding:7px 10px;min-height:36px;color:var(--ink)}
@media(min-width:801px){.scene-frame{height:clamp(280px,38vh,360px)}.japanese-prompt{font-size:clamp(22px,2vw,28px)}}
@media(max-height:800px) and (min-width:801px){.workspace{padding-top:44px}}

/* Horizontal grading is available only on the answer side; keep vertical touch scrolling. */
.card-back{position:relative;touch-action:pan-y pinch-zoom;transition:transform .18s ease-out,border-color .18s,box-shadow .18s}.swipe-hint{display:flex;justify-content:space-between;gap:16px;margin:20px 2px -9px;font-size:11px;line-height:1.6;color:var(--muted);user-select:none}.swipe-hint span{transition:color .14s}.swipe-feedback{position:absolute;top:10px;left:50%;transform:translateX(-50%);pointer-events:none;white-space:nowrap;border:1px solid var(--border);border-radius:20px;background:var(--surface);padding:4px 12px;margin:0;color:#657796;font-size:11px;font-weight:600;box-shadow:0 3px 12px #2336530a}.swipe-feedback[hidden]{display:none}.card-back.is-swiping{transform:translateX(var(--swipe-x,0)) rotate(var(--swipe-rotation,0deg));transition:border-color .14s,box-shadow .14s;user-select:none;cursor:grabbing}.card-back.swipe-right{border-color:#a8bff0}.card-back.swipe-left{border-color:#9eafc9}.swipe-right [data-swipe-grade=mastered]{color:var(--blue);font-weight:650}.swipe-left [data-swipe-grade=again]{color:#586980;font-weight:650}.swipe-right .swipe-feedback{color:var(--blue);background:var(--blue-pale);border-color:#bed0f5}.swipe-left .swipe-feedback{color:#586980;background:#f0f4fa;border-color:#b8c5dc}.card-back.swipe-ready{box-shadow:0 0 0 3px #dce7fc,0 6px 22px #2336530b}.card-back.swipe-ready.swipe-left{box-shadow:0 0 0 3px #e2e8f1,0 6px 22px #2336530b}@media(prefers-reduced-motion:reduce){.card-back.is-swiping{transform:none}}