:root{font-family:Inter,-apple-system,BlinkMacSystemFont,"Segoe UI",Arial,sans-serif;font-synthesis:none;color-scheme:light;--bg:#f5f7f4;--panel:#fff;--panel-soft:#f8faf8;--sidebar:#fdfefd;--text:#172420;--secondary:#4e5c55;--muted:#75817a;--line:#e3e8e4;--accent:#245f4f;--accent-hi:#19684d;--accent-soft:#e4f3e9;--hero:#183c33;--hero-text:#f4fbf5;--grid:#e7ece8;--plot-bg:#fff;--shadow:0 11px 45px rgba(14,48,31,.035)}
:root[data-theme=dark]{color-scheme:dark;--bg:#111816;--panel:#1a2420;--panel-soft:#1e2b25;--sidebar:#161f1a;--text:#eff6ef;--secondary:#b9c9bf;--muted:#9aaca1;--line:#2f3e35;--accent:#87dcb1;--accent-hi:#91e2bb;--accent-soft:#254534;--hero:#234d3b;--hero-text:#f5fbf5;--grid:#33413a;--plot-bg:#1a2420;--shadow:0 11px 45px rgba(0,0,0,.06)}
*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;background:var(--bg);color:var(--text)}button,input,textarea,select{font:inherit}button{cursor:pointer}button:focus-visible,input:focus-visible,textarea:focus-visible,select:focus-visible,[role=button]:focus-visible{outline:3px solid #76bca0;outline-offset:2px}a{color:inherit}.app-shell{min-height:100vh;display:flex}#view{min-width:0;width:100%;flex:1}.sidebar{width:260px;background:var(--sidebar);border-right:1px solid var(--line);height:100dvh;overflow-y:auto;position:sticky;top:0;flex-shrink:0;padding:28px 17px;display:flex;flex-direction:column;gap:2px;z-index:40}.brand{display:flex;align-items:center;gap:11px;padding:6px 11px;margin-bottom:42px}.brand-mark{width:43px;height:43px;display:grid;place-items:center;border-radius:14px;background:#1b493b;color:#d0ffe0;font-size:27px;font-family:Georgia,serif;box-shadow:0 5px 18px #174f3a22}.brand strong{display:block;font-size:21px;font-weight:800;letter-spacing:-.8px}.brand small{display:block;color:var(--muted);font-size:9px;letter-spacing:1.7px;font-weight:800;margin-top:3px}.sidebar-label{color:var(--muted);font-size:10px;font-weight:800;letter-spacing:1.35px;margin:0 12px 13px}.section-label{margin-top:28px}.nav-link{display:flex;align-items:center;gap:12px;border:0;background:transparent;color:var(--secondary);width:100%;text-align:left;padding:12px 11px;border-radius:10px;font-size:13px;font-weight:600;line-height:1.2;transition:background .16s,color .16s}.nav-link span:first-child{font-size:18px;width:23px;text-align:center;color:var(--muted);font-family:Georgia,serif}.nav-link:hover{background:var(--panel-soft);color:var(--text)}.nav-link.active{background:var(--accent-soft);color:var(--accent)}.nav-link.active span:first-child,.nav-link.selected span:first-child{color:var(--accent)}.nav-link.selected{color:var(--accent);background:var(--panel-soft)}.nav-count{margin-left:auto;font-size:11px!important;width:auto!important;font-family:inherit!important;font-weight:700;color:var(--muted)}.sidebar-bottom{margin-top:auto;padding:25px 10px 5px}.mini-badge{font-size:11px;color:var(--accent);font-weight:700;display:flex;align-items:center;gap:7px}.mini-dot,.pulse,.ok-dot{width:7px;height:7px;border-radius:50%;background:#5ac696;display:inline-block;box-shadow:0 0 0 4px #66cba31e}.sidebar-bottom p{font-size:11px;line-height:1.7;color:var(--muted)}.theme-toggle{border:1px solid var(--line);background:var(--panel);border-radius:10px;padding:12px 14px;width:100%;text-align:left;color:var(--secondary);font-size:12px;font-weight:700;margin-top:15px}.theme-toggle span{margin-right:10px;font-size:15px}.main{min-width:0;flex:1;padding:0 42px 26px;max-width:1740px;margin:0 auto;width:100%}.topbar{min-height:87px;display:flex;justify-content:space-between;align-items:center;gap:10px}.breadcrumb,.header-right{font-size:10px;letter-spacing:1.25px;color:var(--muted);font-weight:800}.breadcrumb span{color:#b9c4bb;padding:0 7px}.header-right{color:var(--accent);font-size:9px}.hero{background:var(--hero);border-radius:20px;min-height:320px;position:relative;overflow:hidden;color:var(--hero-text);padding:48px 50px}.hero::after{content:'';position:absolute;width:640px;height:640px;border:1px solid #c8efcd1e;border-radius:50%;top:-300px;right:-80px;pointer-events:none}.hero::before{content:'';position:absolute;width:460px;height:460px;border:1px solid #c8efcd13;border-radius:50%;right:0;top:-200px;pointer-events:none}.hero-eyebrow{font-size:10px;font-weight:800;letter-spacing:2px;display:flex;align-items:center;gap:12px;color:#c3dfcc}.hero h1{font-weight:750;letter-spacing:-2.6px;font-size:clamp(32px,3.6vw,54px);line-height:1.12;margin:25px 0 15px;max-width:750px;position:relative;z-index:2}.hero h1 em{color:#b6eccb;font-style:normal}.hero p{font-size:13px;max-width:550px;color:#c0d6c7;line-height:1.8;position:relative;z-index:2}.hero-chips{display:flex;gap:21px;flex-wrap:wrap;margin-top:26px;position:relative;z-index:2;font-size:11px;color:#c2e3d0;font-weight:600}.hero-art{position:absolute;right:53px;top:35px;width:210px;height:245px;opacity:.5;transform:rotate(5deg);font-family:Georgia,serif;pointer-events:none}.hero-art span{position:absolute;font-size:22px;right:0;top:8px}.hero-art strong{position:absolute;font-size:90px;right:78px;top:50px;font-weight:400;color:#bcf4d0}.hero-art i{position:absolute;bottom:22px;left:2px;font-size:19px}.hero-art b{position:absolute;bottom:0;right:0;font-size:15px;font-weight:normal}.workspace{padding-top:43px}.section-head{display:flex;align-items:end;justify-content:space-between;margin-bottom:22px;gap:16px}.overline{font-size:10px;font-weight:800;letter-spacing:1.8px;color:var(--accent)}.section-head h2{font-size:30px;letter-spacing:-1.2px;margin:10px 0 9px}.section-head p,.detail-wrap>p{color:var(--muted);font-size:13px;line-height:1.7;margin:0}.count-pill{white-space:nowrap;border:1px solid var(--line);border-radius:100px;padding:8px 14px;font-size:11px;color:var(--secondary);background:var(--panel);font-weight:700}.search-wrap{position:relative}.search-wrap>span{position:absolute;left:20px;top:12px;font-size:24px;color:var(--muted)}.search-wrap input{display:block;width:100%;height:52px;border:1px solid var(--line);border-radius:12px;background:var(--panel);color:var(--text);padding:0 85px 0 53px;font-size:13px;box-shadow:var(--shadow)}.search-wrap input::placeholder{color:var(--muted)}.search-wrap kbd{position:absolute;right:15px;top:14px;border:1px solid var(--line);background:var(--panel-soft);border-radius:5px;padding:5px 7px;color:var(--muted);font-size:10px}.filters{display:flex;gap:8px;overflow-x:auto;padding:16px 0 4px;scrollbar-width:thin}.filter{white-space:nowrap;border:1px solid var(--line);background:var(--panel);color:var(--secondary);border-radius:100px;padding:9px 14px;font-size:11px;font-weight:700}.filter:hover{border-color:#a4bdb0}.filter.active{background:var(--accent);border-color:var(--accent);color:var(--bg)}:root[data-theme=dark] .filter.active{color:#162a20}.category-section{margin-top:30px}.category-heading{display:flex;align-items:center;gap:12px;margin-bottom:14px}.category-symbol{border:1px solid var(--line);border-radius:9px;width:33px;height:33px;display:grid;place-items:center;color:var(--accent);font-size:19px;font-family:Georgia,serif;background:var(--panel)}.category-heading h3{font-size:16px;letter-spacing:-.4px;margin:0}.category-heading>span:last-child{color:var(--muted);font-size:11px}.card-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:14px}.tool-card{background:var(--panel);border:1px solid var(--line);border-radius:15px;padding:23px;min-height:201px;transition:transform .2s,border-color .2s,box-shadow .2s;cursor:pointer;outline-offset:1px;position:relative}.tool-card:hover{transform:translateY(-3px);border-color:#a8cabc;box-shadow:0 15px 40px #173d2710}.card-top{display:flex;align-items:start;justify-content:space-between;margin-bottom:23px}.tool-icon{display:inline-grid;place-items:center;width:41px;height:41px;background:var(--accent-soft);border-radius:11px;color:var(--accent);font-family:Georgia,serif;font-size:21px;line-height:1}.fav-btn{background:transparent;border:0;color:#adbab2;font-size:23px;line-height:1;border-radius:7px;padding:4px}.fav-btn:hover,.fav-btn.is-fav{color:#e1a650}.card-label{color:var(--accent);font-size:9px;font-weight:800;letter-spacing:1.3px;line-height:1.4}.tool-card h3{font-size:17px;line-height:1.3;letter-spacing:-.5px;margin:10px 0 9px;display:flex;justify-content:space-between;gap:8px}.tool-card .arrow{font-size:19px;color:var(--muted);font-weight:400;transition:transform .2s}.tool-card:hover .arrow{transform:translate(3px,-3px)}.tool-card p{font-size:12px;line-height:1.7;color:var(--muted);margin:0}.footer{padding:40px 0 20px;margin-top:45px;border-top:1px solid var(--line);display:flex;gap:18px;align-items:center;color:var(--muted);font-size:10px}.footer b{font-size:15px;color:var(--accent)}.footer span:last-child{margin-left:auto}.empty{border:1px dashed var(--line);border-radius:15px;padding:65px 25px;text-align:center;color:var(--muted);font-size:14px;margin-top:20px}.empty h3{color:var(--text);margin-bottom:5px}.small-btn{background:var(--accent-soft);color:var(--accent);border:1px solid var(--line);border-radius:9px;padding:10px 17px;font-size:12px;font-weight:700;margin-top:13px}.small-btn.danger{background:var(--panel);color:#ab6565}.small-btn:disabled{opacity:.4;cursor:not-allowed}
/* work */
.back-link,.detail-back{background:none;border:0;color:var(--accent);font-size:12px;font-weight:750}.detail-wrap{max-width:1300px;margin:18px auto}.detail-back{padding:6px 0;margin-bottom:26px}.tool-heading{display:flex;align-items:center;gap:23px;margin-bottom:36px}.tool-big-icon{width:74px;height:74px;border-radius:18px;background:var(--accent-soft);display:grid;place-items:center;font-family:Georgia,serif;font-size:40px;color:var(--accent);flex-shrink:0}.tool-heading h1{font-size:clamp(26px,3vw,38px);letter-spacing:-1.4px;margin:8px 0}.tool-heading p{font-size:13px;color:var(--muted);line-height:1.5;margin:0}.tool-heading .big{margin-left:auto;font-size:30px}.work-grid{display:grid;grid-template-columns:minmax(270px,.96fr) minmax(310px,1.04fr);gap:16px;align-items:start}.work-panel,.answer-panel{background:var(--panel);border:1px solid var(--line);border-radius:16px;min-height:440px;overflow:hidden;box-shadow:var(--shadow)}.panel-heading{display:flex;align-items:center;justify-content:space-between;gap:12px;padding:23px 25px;border-bottom:1px solid var(--line)}.panel-heading strong{font-size:11px;letter-spacing:1px}.panel-heading>span{font-size:10px;color:var(--muted)}.fields{padding:25px;display:grid;gap:18px}.input-group{display:flex;flex-direction:column;gap:9px}.input-group>span{font-size:12px;font-weight:700;color:var(--secondary)}.input-group input,.input-group textarea,.input-group select{width:100%;border:1px solid var(--line);background:var(--panel-soft);color:var(--text);padding:13px 15px;border-radius:9px;font-size:14px;transition:border-color .2s;font-family:ui-monospace,"SFMono-Regular",Consolas,monospace;line-height:1.5}.input-group textarea{resize:vertical;min-height:93px}.input-group input:focus,.input-group textarea:focus,.input-group select:focus{border-color:#63ac88}.form-actions{display:flex;gap:9px;padding:0 25px 25px}.submit-btn{border:0;border-radius:9px;padding:15px 20px;background:var(--accent);color:var(--bg);font-size:13px;font-weight:800;flex:1;display:flex;align-items:center;justify-content:space-between;gap:35px}:root[data-theme=dark] .submit-btn{color:#0c1d14}.submit-btn:hover{filter:brightness(1.1)}.submit-btn span{font-size:17px}.reset-btn{border:1px solid var(--line);background:var(--panel-soft);color:var(--secondary);padding:14px 18px;border-radius:9px;font-size:12px;font-weight:700}.suggestions{margin:0 25px;padding:22px 0;border-top:1px solid var(--line)}.suggestions strong{font-size:9px;letter-spacing:1.3px;color:var(--muted)}.suggestions>div{display:flex;flex-wrap:wrap;gap:7px;margin-top:11px}.suggestions span{border-radius:7px;background:var(--panel-soft);border:1px solid var(--line);color:var(--secondary);padding:7px 10px;font-size:10px}.copy-btn{font-size:11px;font-weight:700;border:1px solid var(--line);border-radius:8px;background:var(--panel-soft);color:var(--secondary);padding:8px 11px}.copy-btn:disabled{opacity:.45;cursor:not-allowed}.result-idle{text-align:center;color:var(--muted);max-width:290px;margin:92px auto 40px;padding:0 22px}.idle-glyph{font-family:Georgia,serif;font-size:54px;color:var(--accent);opacity:.25}.result-idle h3{font-size:17px;color:var(--secondary);margin:15px 0 7px}.result-idle p{font-size:12px;line-height:1.7}.result-content{padding:26px}.result-label{font-size:10px;color:var(--accent);font-weight:800;letter-spacing:1.35px;display:flex;align-items:center;gap:12px}.answer{font-family:ui-monospace,"SFMono-Regular",Consolas,monospace;white-space:normal;overflow-wrap:anywhere;line-height:1.65;font-size:clamp(17px,1.7vw,24px);font-weight:650;padding:22px 0 27px;border-bottom:1px solid var(--line);color:var(--text);font-variant-numeric:tabular-nums}.solution-steps{margin-top:24px}.steps-label{font-size:9px;color:var(--muted);font-weight:800;letter-spacing:1.45px;margin-bottom:15px}.step{display:flex;gap:14px;align-items:baseline;padding:9px 0;color:var(--secondary);font-size:12px;line-height:1.75;border-bottom:1px solid var(--line);white-space:pre-wrap;overflow-wrap:anywhere}.step>span{font-family:ui-monospace,monospace;color:var(--accent);font-size:10px;font-weight:750}.step:last-child{border-bottom:0}.result-note{margin-top:21px;display:flex;align-items:baseline;gap:12px;background:var(--accent-soft);border-radius:9px;padding:10px 15px;color:var(--accent)}.result-note p{font-size:11px;line-height:1.7;margin:0}.result-error{padding:63px 35px;text-align:center}.result-error>span{display:inline-grid;place-items:center;width:53px;height:53px;background:#ffeee9;color:#a94631;font-size:25px;font-weight:700;border-radius:50%}.result-error h3{font-size:18px;margin:17px 0 9px}.result-error p{color:#ba5748;font-size:13px;line-height:1.65;overflow-wrap:anywhere}.result-error small{color:var(--muted);font-size:11px}.note-strip{display:flex;align-items:center;gap:16px;background:var(--panel);border:1px solid var(--line);padding:17px 22px;border-radius:12px;margin-top:19px}.note-strip>span{font-size:24px;color:var(--accent)}.note-strip p{margin:0;font-size:11px;line-height:1.7;color:var(--muted)}.note-strip b{color:var(--secondary)}.plot-container{position:relative;height:340px;min-width:0;width:100%;border:1px solid var(--line);border-radius:10px;margin-top:17px;overflow:hidden}.plot-container canvas{width:100%;height:100%;display:block}.plot-controls{position:absolute;top:12px;right:12px;display:flex;flex-direction:column;gap:4px}.plot-controls button{width:31px;height:31px;background:var(--panel);color:var(--text);border:1px solid var(--line);border-radius:5px;font-size:17px}.plot-legend{display:flex;flex-wrap:wrap;gap:12px;font-size:11px;margin:12px 0}.plot-legend span{display:flex;gap:6px;align-items:center;color:var(--secondary)}.plot-legend i{width:10px;height:10px;border-radius:100%}.history-wrap{padding-top:50px;max-width:1000px;margin:0 auto}.history-wrap h1{font-size:35px;letter-spacing:-1.2px;margin:8px 0}.history-wrap>p{color:var(--muted);font-size:13px}.history-list{margin-top:24px;border:1px solid var(--line);background:var(--panel);border-radius:14px;overflow:hidden}.history-entry{display:flex;align-items:center;gap:15px;padding:16px 20px;width:100%;text-align:left;border:0;border-bottom:1px solid var(--line);background:transparent;color:var(--text)}.history-entry:hover{background:var(--panel-soft)}.history-entry:last-child{border-bottom:0}.history-entry>span:nth-child(2){display:flex;flex-direction:column;gap:6px;min-width:150px}.history-entry b{font-size:12px}.history-entry small{color:var(--muted);font-size:10px}.history-entry>strong{margin-left:auto;font-size:12px;color:var(--accent);font-family:monospace;text-align:right;max-width:32%;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}.mobile-overlay,.mobile-menu,.mobile-close{display:none}.icon-btn{background:transparent;border:0;color:var(--text);font-size:24px}.skip-link{position:absolute;top:-50px;left:10px;background:#fff;z-index:100;padding:10px}.skip-link:focus{top:10px}.noscript{position:fixed;bottom:15px;left:15px;background:#ffe7a4;padding:15px;color:#000;z-index:99}
@media(min-width:1450px){.card-grid{grid-template-columns:repeat(4,minmax(0,1fr))}.hero-art{right:80px;transform:scale(1.2)}}
@media(max-width:1120px){.sidebar{width:236px}.main{padding:0 24px 20px}.card-grid{grid-template-columns:repeat(2,minmax(0,1fr))}.hero-art{opacity:.25}.work-grid{grid-template-columns:1fr 1fr}.panel-heading{padding:20px}.fields{padding:20px}.form-actions{padding:0 20px 20px}}
@media(max-width:790px){.sidebar{position:fixed;top:0;bottom:0;left:0;transform:translateX(-120%);visibility:hidden;pointer-events:none;transition:transform .24s;width:min(295px,86vw);height:100dvh;box-shadow:12px 0 35px #0002}.sidebar.open{transform:translateX(0);visibility:visible;pointer-events:auto}.mobile-overlay.visible{display:block;position:fixed;inset:0;background:#06100ca8;z-index:35}.mobile-close{display:block;position:absolute;right:8px;top:32px}.mobile-menu{display:block;font-size:20px}.main{padding:0 21px 18px}.topbar{min-height:70px;justify-content:initial}.header-right{margin-left:auto}.hero{min-height:290px;padding:40px 30px}.hero h1{font-size:clamp(31px,6vw,45px)}.hero-art{right:0;opacity:.15}.work-grid{grid-template-columns:1fr}.work-panel,.answer-panel{min-height:0}.result-idle{margin:38px auto 55px}.tool-heading{margin-bottom:25px}.detail-wrap{margin-top:12px}}
@media(max-width:520px){.main{padding:0 15px 15px}.breadcrumb,.header-right{font-size:9px}.header-right{display:none}.hero{padding:32px 25px;border-radius:14px;min-height:300px}.hero h1{font-size:34px;letter-spacing:-1.4px;line-height:1.16}.hero h1 br{display:none}.hero p{font-size:12px}.hero-chips{gap:8px 15px;margin-top:20px;font-size:10px}.hero-art{display:none}.workspace{padding-top:34px}.section-head h2{font-size:25px}.section-head p{font-size:11px}.count-pill{display:none}.search-wrap input{height:50px;padding-right:20px;font-size:12px}.search-wrap kbd{display:none}.filters{margin:0 -15px;padding:15px 15px 5px}.card-grid{grid-template-columns:1fr;gap:9px}.tool-card{min-height:172px;padding:18px}.card-top{margin-bottom:13px}.tool-card h3{font-size:16px}.category-section{margin-top:26px}.category-heading h3{font-size:15px}.footer{flex-wrap:wrap;gap:9px 12px}.footer span:last-child{margin-left:0}.tool-heading{gap:12px}.tool-big-icon{width:52px;height:52px;font-size:29px;border-radius:12px}.tool-heading h1{font-size:25px}.tool-heading p{font-size:11px}.tool-heading .overline{font-size:8px}.tool-heading .big{font-size:22px}.panel-heading{padding:18px}.fields{padding:18px}.form-actions{padding:0 18px 18px}.suggestions{margin:0 18px}.result-content{padding:19px}.answer{font-size:18px}.plot-container{height:250px}.note-strip{align-items:flex-start}.history-entry{gap:9px;padding:12px}.history-entry .tool-icon{width:34px;height:34px}.history-entry>strong{max-width:25%;font-size:10px}}
@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}*,*:before,*:after{transition:none!important;animation:none!important}}
/* Version 2: keyboard, clickable worked examples and history export. */
.math-keyboard{margin:0 25px 20px;padding:14px 15px;background:var(--panel-soft);border:1px solid var(--line);border-radius:11px}
.math-keyboard>span,.sample-strip>strong{font-size:9px;letter-spacing:1.2px;color:var(--muted);font-weight:800}
.math-keyboard>div{display:flex;flex-wrap:wrap;gap:6px;margin-top:12px}
.math-key{min-width:38px;padding:9px 11px;background:var(--panel);border:1px solid var(--line);color:var(--secondary);border-radius:7px;font:600 12px ui-monospace,Consolas,monospace}
.math-key:hover{background:var(--accent-soft);color:var(--accent);border-color:var(--accent)}
.sample-strip{margin:0 25px;padding:21px 0 12px;border-top:1px solid var(--line)}
.sample-strip>div{display:flex;flex-wrap:wrap;gap:8px;margin-top:11px}
.sample-btn{background:var(--accent-soft);color:var(--accent);border:1px solid transparent;border-radius:8px;padding:10px 12px;font-size:11px;font-weight:700;text-align:left}
.sample-btn:hover{border-color:var(--accent)}
@media(max-width:520px){.math-keyboard,.sample-strip{margin-left:18px;margin-right:18px}.math-key{padding:10px 13px}.sample-btn{flex:1}}

/* v5 help text and language selector */
.lang-control{padding:12px 14px 16px;margin:0 5px 8px;border-bottom:1px solid var(--border, #dde8e1);display:flex;flex-direction:column;gap:6px}
.lang-control label{font-size:11px;font-weight:650;opacity:.75}
.lang-control select{width:100%;min-width:0;background:var(--surface, #fff);color:var(--text, #26352d);border:1px solid var(--border, #c7d6ce);padding:9px 8px;border-radius:9px;font-weight:650;cursor:pointer}
.field-help{display:block;font-size:12px;line-height:1.55;color:var(--muted, #6c8175);font-weight:400;margin-top:7px;overflow-wrap:anywhere;white-space:normal}
@media(max-width:750px){.lang-control{padding:10px 8px 12px;margin:0 0 4px}.lang-control select{padding:7px 5px;font-size:12px}.field-help{font-size:11.5px}}

.mobile-language{display:none;margin-left:auto;align-items:center}
.mobile-language select{background:var(--surface,#fff);border:1px solid var(--border,#cbd9d0);border-radius:8px;color:var(--text,#172c24);font-weight:750;padding:8px 5px;font-size:12px}
@media(max-width:790px){.mobile-language{display:flex}.mobile-language select{max-width:60px}.topbar{gap:8px}.topbar .header-right{display:none}}

.sr-only{position:absolute!important;width:1px!important;height:1px!important;padding:0!important;margin:-1px!important;overflow:hidden!important;clip:rect(0,0,0,0)!important;white-space:nowrap!important;border:0!important}
@media(max-width:790px){.topbar .breadcrumb,.topbar .back-link{display:none}.mobile-language{margin-left:auto}}