.app{display:grid;grid-template-columns:var(--rail-w) 1fr;height:100dvh;overflow:hidden}.rail{display:flex;flex-direction:column;align-items:center;gap:var(--sp-2);padding:var(--sp-3) 0 var(--sp-4);background:linear-gradient(180deg,var(--bg-deep),var(--bg) 60%);border-right:1px solid var(--border);z-index:var(--z-sticky)}.rail-brand{margin-bottom:var(--sp-2)}.rail-brand-mark{display:grid;place-items:center;width:42px;height:42px;border-radius:var(--r-md);color:#060b14;background:linear-gradient(145deg,var(--brand-bright),var(--brand-dim));box-shadow:0 6px 18px -6px var(--subject-glow)}.rail-group{display:flex;flex-direction:column;gap:var(--sp-1);width:100%;align-items:center}.rail-divider{width:28px;height:1px;background:var(--border);margin:var(--sp-2) 0}.rail-spacer{flex:1}.rail-link{position:relative;display:grid;place-items:center;width:46px;height:46px;border-radius:var(--r-md);color:var(--ink-3);transition:color var(--dur-2) var(--ease-out-quart),background var(--dur-2) var(--ease-out-quart)}.rail-link:hover{color:var(--ink);background:var(--surface)}.rail-link.active{color:var(--subject-bright, var(--brand-bright));background:color-mix(in oklch,var(--subject, var(--brand)) 16%,var(--surface))}.rail-link[data-subject].active{color:var(--subject-bright)}.rail-link.active:before{content:"";position:absolute;left:-8px;top:50%;transform:translateY(-50%);width:3px;height:22px;border-radius:var(--r-pill);background:var(--subject, var(--brand));box-shadow:0 0 12px 1px var(--subject, var(--brand))}.rail-tip{position:fixed;left:calc(var(--rail-w) + 6px);transform:translate(-6px);padding:4px 10px;background:var(--surface-3);border:1px solid var(--border-strong);border-radius:var(--r-sm);font-size:var(--fs-xs);font-weight:550;white-space:nowrap;color:var(--ink);opacity:0;pointer-events:none;box-shadow:var(--sh-2);transition:opacity var(--dur-1),transform var(--dur-1) var(--ease-out-quart);z-index:var(--z-tooltip)}.rail-link:hover .rail-tip{opacity:1;transform:translate(0)}.rail-cmd{font-family:var(--font-mono);font-size:var(--fs-xs);color:var(--ink-3);border:1px solid var(--border);border-radius:var(--r-sm);padding:6px 7px;background:var(--surface)}.rail-cmd:hover{color:var(--ink);border-color:var(--border-strong)}.app-body{display:flex;flex-direction:column;min-width:0;height:100dvh}.topbar{display:flex;align-items:center;justify-content:space-between;gap:var(--sp-4);height:60px;padding:0 clamp(1rem,3vw,2rem);border-bottom:1px solid var(--border);background:color-mix(in oklch,var(--bg) 80%,transparent);backdrop-filter:blur(12px);z-index:var(--z-sticky);flex-shrink:0}.breadcrumb{display:flex;align-items:center;gap:var(--sp-2);font-size:var(--fs-sm);color:var(--ink-2);min-width:0;overflow:hidden;white-space:nowrap}.breadcrumb-root{font-weight:600;color:var(--ink)}.breadcrumb-seg{display:inline-flex;gap:var(--sp-2);text-transform:capitalize}.breadcrumb-seg:last-child{color:var(--subject-ink, var(--ink));font-weight:550}.breadcrumb-sep{color:var(--ink-faint)}.topbar-actions{display:flex;align-items:center;gap:var(--sp-3)}.topbar-search{display:flex;align-items:center;gap:var(--sp-5);padding:.5em .7em .5em .9em;border:1px solid var(--border);border-radius:var(--r-md);background:var(--surface);color:var(--ink-3);font-size:var(--fs-sm);min-width:220px;justify-content:space-between}.topbar-search:hover{border-color:var(--border-strong);color:var(--ink-2)}.topbar-search kbd{font-size:var(--fs-xs);padding:2px 6px;border:1px solid var(--border-strong);border-radius:var(--r-xs);background:var(--surface-2)}@media (max-width: 720px){.topbar-search span{display:none}.topbar-search{min-width:0}}.app-main{flex:1;overflow-y:auto;overflow-x:hidden;scroll-behavior:smooth}.study-timer{display:flex;align-items:center;gap:var(--sp-2);padding:5px 8px 5px 11px;border:1px solid var(--border);border-radius:var(--r-md);background:var(--surface)}.study-timer[data-running=true]{border-color:color-mix(in oklch,var(--subject) 50%,var(--border));background:color-mix(in oklch,var(--subject) 10%,var(--surface))}.study-timer-icon{color:var(--subject-ink, var(--brand))}.study-timer[data-running=true] .study-timer-icon{animation:timer-pulse 2s var(--ease-in-out) infinite}@keyframes timer-pulse{50%{opacity:.45}}.study-timer-clock{font-family:var(--font-mono);font-size:var(--fs-sm);font-weight:600;letter-spacing:.02em;color:var(--ink);font-variant-numeric:tabular-nums;min-width:44px}.study-timer-btn{display:grid;place-items:center;width:26px;height:26px;border-radius:var(--r-sm);color:var(--ink-2)}.study-timer-btn:hover:not(:disabled){background:var(--surface-2);color:var(--ink)}.study-timer-btn:disabled{opacity:.35;cursor:not-allowed}.cmdk-backdrop{position:fixed;inset:0;z-index:var(--z-cmdk);background:#02030699;backdrop-filter:blur(4px);display:flex;align-items:flex-start;justify-content:center;padding-top:14vh;animation:cmdk-fade var(--dur-2) var(--ease-out-quart)}@keyframes cmdk-fade{0%{opacity:0}}.cmdk{width:min(620px,92vw);background:var(--surface-2);border:1px solid var(--border-strong);border-radius:var(--r-lg);box-shadow:var(--sh-3);overflow:hidden;animation:cmdk-rise var(--dur-3) var(--ease-out-expo)}@keyframes cmdk-rise{0%{transform:translateY(-12px) scale(.985);opacity:0}}.cmdk-input-row{display:flex;align-items:center;gap:var(--sp-3);padding:var(--sp-4) var(--sp-4);border-bottom:1px solid var(--border);color:var(--ink-3)}.cmdk-input-row input{flex:1;background:none;border:none;outline:none;font-size:1.05rem;color:var(--ink)}.cmdk-input-row input::placeholder{color:var(--ink-3)}.cmdk-input-row kbd{font-size:var(--fs-xs);padding:2px 7px;border:1px solid var(--border-strong);border-radius:var(--r-xs);color:var(--ink-3)}.cmdk-list{max-height:50vh;overflow-y:auto;padding:var(--sp-2)}.cmdk-empty{padding:var(--sp-6);text-align:center;color:var(--ink-3)}.cmdk-item{display:flex;align-items:center;gap:var(--sp-3);padding:var(--sp-2) var(--sp-3);border-radius:var(--r-sm);cursor:pointer}.cmdk-item[data-active=true]{background:color-mix(in oklch,var(--subject, var(--brand)) 16%,var(--surface-3))}.cmdk-item-icon{display:grid;place-items:center;width:30px;height:30px;border-radius:var(--r-sm);background:var(--surface-3);color:var(--subject-ink, var(--ink-2));flex-shrink:0}.cmdk-item-text{display:flex;flex-direction:column;min-width:0;flex:1}.cmdk-item-label{font-weight:550;color:var(--ink)}.cmdk-item-sub{font-size:var(--fs-xs);color:var(--ink-3);overflow:hidden;text-overflow:ellipsis;white-space:nowrap;max-width:46ch}.cmdk-item-kind{font-size:var(--fs-xs);color:var(--ink-faint);text-transform:uppercase;letter-spacing:.04em}.cmdk-enter{color:var(--subject-ink, var(--brand))}.route-fallback{display:flex;flex-direction:column;align-items:center;justify-content:center;gap:var(--sp-4);height:60vh;color:var(--ink-3)}.route-fallback-pulse{width:38px;height:38px;border-radius:50%;border:3px solid var(--border);border-top-color:var(--subject, var(--brand));animation:spin .8s linear infinite}@keyframes spin{to{transform:rotate(360deg)}}@media (max-width: 640px){.app{grid-template-columns:1fr;grid-template-rows:1fr auto}.rail{grid-row:2;flex-direction:row;width:100%;height:60px;padding:0 var(--sp-3);border-right:none;border-top:1px solid var(--border);overflow-x:auto}.rail-brand,.rail-divider,.rail-spacer,.rail-cmd{display:none}.rail-group{flex-direction:row;width:auto}.rail-link.active:before{left:50%;top:auto;bottom:-4px;transform:translate(-50%);width:20px;height:3px}.rail-tip{display:none}.app-body{grid-row:1;height:auto;overflow:hidden}}:root{--bg: oklch(.158 .011 256);--bg-deep: oklch(.132 .012 256);--surface: oklch(.196 .012 256);--surface-2: oklch(.232 .013 256);--surface-3: oklch(.272 .014 256);--surface-hover: oklch(.252 .014 256);--border: oklch(.3 .013 256);--border-strong: oklch(.38 .016 256);--border-faint: oklch(.26 .012 256 / .7);--ink: oklch(.97 .004 256);--ink-1: oklch(.9 .006 256);--ink-2: oklch(.785 .011 256);--ink-3: oklch(.665 .013 256);--ink-faint: oklch(.54 .013 256);--brand: oklch(.74 .115 200);--brand-bright: oklch(.82 .13 198);--brand-dim: oklch(.5 .08 202);--good: oklch(.78 .15 152);--good-dim: oklch(.5 .1 152);--warn: oklch(.82 .15 84);--bad: oklch(.69 .18 24);--bad-dim: oklch(.48 .13 24);--physics: oklch(.78 .123 205);--physics-bright: oklch(.86 .14 203);--physics-dim: oklch(.52 .085 206);--physics-ink: oklch(.88 .09 205);--physics-h: 205;--maths: oklch(.7 .135 262);--maths-bright: oklch(.78 .15 262);--maths-dim: oklch(.5 .1 264);--maths-ink: oklch(.82 .1 262);--maths-h: 262;--fmaths: oklch(.72 .15 312);--fmaths-bright: oklch(.8 .16 310);--fmaths-dim: oklch(.52 .115 314);--fmaths-ink: oklch(.84 .11 312);--fmaths-h: 312;--econ: oklch(.8 .135 70);--econ-bright: oklch(.87 .145 75);--econ-dim: oklch(.56 .1 66);--econ-ink: oklch(.86 .1 72);--econ-h: 70;--subject: var(--brand);--subject-bright: var(--brand-bright);--subject-dim: var(--brand-dim);--subject-ink: var(--brand-bright);--subject-h: 200;--subject-glow: oklch(.74 .115 200 / .22);--font-display: "Fraunces", "Iowan Old Style", Georgia, serif;--font-sans: "Inter", system-ui, -apple-system, "Segoe UI", sans-serif;--font-mono: "JetBrains Mono", "SF Mono", ui-monospace, monospace;--fs-display: clamp(2.4rem, 1.6rem + 3.4vw, 4.2rem);--fs-h1: clamp(1.9rem, 1.4rem + 2vw, 2.9rem);--fs-h2: clamp(1.45rem, 1.2rem + 1vw, 1.95rem);--fs-h3: clamp(1.18rem, 1.05rem + .55vw, 1.42rem);--fs-body: 1rem;--fs-sm: .875rem;--fs-xs: .78rem;--sp-1: .25rem;--sp-2: .5rem;--sp-3: .75rem;--sp-4: 1rem;--sp-5: 1.5rem;--sp-6: 2rem;--sp-7: 3rem;--sp-8: 4.5rem;--sp-9: 6.5rem;--r-xs: 6px;--r-sm: 9px;--r-md: 13px;--r-lg: 18px;--r-xl: 26px;--r-pill: 999px;--sh-1: 0 1px 2px oklch(0 0 0 / .4);--sh-2: 0 4px 14px -4px oklch(0 0 0 / .5), 0 2px 5px -2px oklch(0 0 0 / .4);--sh-3: 0 18px 44px -14px oklch(0 0 0 / .62), 0 6px 16px -8px oklch(0 0 0 / .5);--sh-glow: 0 0 0 1px var(--subject-glow), 0 8px 34px -10px var(--subject-glow);--ease-out-quart: cubic-bezier(.25, 1, .5, 1);--ease-out-expo: cubic-bezier(.16, 1, .3, 1);--ease-in-out: cubic-bezier(.65, 0, .35, 1);--dur-1: .12s;--dur-2: .22s;--dur-3: .38s;--dur-4: .6s;--z-base: 1;--z-raised: 10;--z-sticky: 100;--z-dropdown: 200;--z-backdrop: 300;--z-modal: 400;--z-toast: 500;--z-tooltip: 600;--z-cmdk: 700;--rail-w: 76px;--max-content: 1180px}[data-subject=physics]{--subject: var(--physics);--subject-bright: var(--physics-bright);--subject-dim: var(--physics-dim);--subject-ink: var(--physics-ink);--subject-h: var(--physics-h);--subject-glow: oklch(.78 .123 205 / .22)}[data-subject=maths]{--subject: var(--maths);--subject-bright: var(--maths-bright);--subject-dim: var(--maths-dim);--subject-ink: var(--maths-ink);--subject-h: var(--maths-h);--subject-glow: oklch(.7 .135 262 / .24)}[data-subject=fmaths]{--subject: var(--fmaths);--subject-bright: var(--fmaths-bright);--subject-dim: var(--fmaths-dim);--subject-ink: var(--fmaths-ink);--subject-h: var(--fmaths-h);--subject-glow: oklch(.72 .15 312 / .24)}[data-subject=economics]{--subject: var(--econ);--subject-bright: var(--econ-bright);--subject-dim: var(--econ-dim);--subject-ink: var(--econ-ink);--subject-h: var(--econ-h);--subject-glow: oklch(.8 .135 70 / .22)}*,*:before,*:after{box-sizing:border-box}*{margin:0;padding:0}html{-webkit-text-size-adjust:100%;scroll-behavior:smooth;scrollbar-gutter:stable}@media (prefers-reduced-motion: reduce){html{scroll-behavior:auto}}body{font-family:var(--font-sans);font-size:var(--fs-body);line-height:1.6;color:var(--ink-1);background:var(--bg);-webkit-font-smoothing:antialiased;text-rendering:optimizeLegibility;font-feature-settings:"cv05" 1,"ss01" 1;overflow-x:hidden}body:before{content:"";position:fixed;inset:0;z-index:-2;background:radial-gradient(60vw 50vh at 78% -8%,var(--subject-glow),transparent 60%),radial-gradient(48vw 44vh at 6% 8%,oklch(.3 .04 256 / .5),transparent 62%);opacity:.7;transition:background var(--dur-4) var(--ease-out-quart);pointer-events:none}body:after{content:"";position:fixed;inset:0;z-index:-1;pointer-events:none;opacity:.025;background-image:url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='160' height='160'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.85' numOctaves='2' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E")}h1,h2,h3,h4{font-family:var(--font-display);font-weight:600;line-height:1.08;letter-spacing:-.02em;color:var(--ink);text-wrap:balance}h1{font-size:var(--fs-h1)}h2{font-size:var(--fs-h2)}h3{font-size:var(--fs-h3);letter-spacing:-.015em}p{text-wrap:pretty;max-width:72ch}a{color:inherit;text-decoration:none}button{font:inherit;color:inherit;cursor:pointer;border:none;background:none}input,select,textarea{font:inherit;color:inherit}ul,ol{list-style:none}img,svg{display:block;max-width:100%}code,kbd{font-family:var(--font-mono);font-size:.92em}:focus-visible{outline:2px solid var(--subject-bright);outline-offset:2px;border-radius:var(--r-xs)}::selection{background:var(--subject-dim);color:var(--ink)}::-webkit-scrollbar{width:11px;height:11px}::-webkit-scrollbar-track{background:transparent}::-webkit-scrollbar-thumb{background:var(--surface-3);border-radius:var(--r-pill);border:3px solid var(--bg)}::-webkit-scrollbar-thumb:hover{background:var(--border-strong)}.container{width:100%;max-width:var(--max-content);margin-inline:auto;padding-inline:clamp(1rem,4vw,2.5rem)}.eyebrow-num{font-family:var(--font-mono);font-size:var(--fs-xs);letter-spacing:.02em;color:var(--subject-ink)}.surface-card{background:linear-gradient(180deg,var(--surface) 0%,var(--surface-2) 140%);border:1px solid var(--border);border-radius:var(--r-lg);box-shadow:var(--sh-2)}.chip{display:inline-flex;align-items:center;gap:var(--sp-2);padding:.28em .7em;border-radius:var(--r-pill);font-size:var(--fs-xs);font-weight:550;letter-spacing:.01em;border:1px solid var(--border);background:var(--surface-2);color:var(--ink-2);white-space:nowrap}.chip[data-tone=subject]{border-color:color-mix(in oklch,var(--subject) 38%,transparent);background:color-mix(in oklch,var(--subject) 13%,var(--surface));color:var(--subject-ink)}.btn{--_bg: var(--surface-2);--_fg: var(--ink-1);display:inline-flex;align-items:center;justify-content:center;gap:var(--sp-2);padding:.62em 1.1em;border-radius:var(--r-md);font-size:var(--fs-sm);font-weight:560;background:var(--_bg);color:var(--_fg);border:1px solid var(--border);transition:transform var(--dur-1) var(--ease-out-quart),background var(--dur-2) var(--ease-out-quart),border-color var(--dur-2) var(--ease-out-quart)}.btn:hover{background:var(--surface-hover);border-color:var(--border-strong)}.btn:active{transform:translateY(1px) scale(.99)}.btn[data-variant=primary]{--_bg: var(--subject);--_fg: oklch(.16 .02 256);border-color:transparent;font-weight:620;box-shadow:0 6px 18px -8px var(--subject-glow)}.btn[data-variant=primary]:hover{--_bg: var(--subject-bright)}.btn[data-variant=ghost]{--_bg: transparent;border-color:transparent}.btn[data-variant=ghost]:hover{--_bg: var(--surface-2)}.btn[data-size=sm]{padding:.4em .75em;font-size:var(--fs-xs)}.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}.katex{font-size:1.04em}.katex-display{margin:var(--sp-4) 0;overflow-x:auto;overflow-y:hidden;padding-bottom:2px}.skip-link{position:fixed;top:-60px;left:var(--sp-4);z-index:var(--z-tooltip);background:var(--surface-3);color:var(--ink);padding:var(--sp-2) var(--sp-4);border-radius:var(--r-sm);border:1px solid var(--border-strong);transition:top var(--dur-2) var(--ease-out-quart)}.skip-link:focus{top:var(--sp-4)}@keyframes reveal-up{0%{opacity:0;transform:translateY(16px)}to{opacity:1;transform:none}}@keyframes reveal-scale{0%{opacity:0;transform:scale(.97)}to{opacity:1;transform:none}}.reveal{animation:reveal-up var(--dur-4) var(--ease-out-expo) both}.reveal-scale{animation:reveal-scale var(--dur-4) var(--ease-out-expo) both}@media (prefers-reduced-motion: reduce){*,*:before,*:after{animation-duration:.001ms!important;animation-iteration-count:1!important;transition-duration:.001ms!important}.reveal,.reveal-scale{animation:none;opacity:1;transform:none}}