/* maths.free — paper + ink + indigo. Bootstrap 5 underneath for the grid/nav/forms. */
:root {
  --paper: #fbfaf7; --paper-2: #f3f1ea; --ink: #141a2b; --ink-2: #4a5169; --ink-3: #8b90a3;
  --line: #e4e1d8; --indigo: #2f4bd6; --indigo-2: #1d33a6; --indigo-soft: #e9edfc;
  --amber: #e8a53c; --amber-soft: #fff4dd; --green: #1f9d6d; --red: #c8452c;
  --radius: 14px; --shadow: 0 1px 2px rgba(20,26,43,.06), 0 10px 30px -18px rgba(20,26,43,.25);
  --bs-primary: var(--indigo); --bs-primary-rgb: 47,75,214; --bs-body-bg: var(--paper); --bs-body-color: var(--ink);
  --bs-link-color: var(--indigo); --bs-link-hover-color: var(--indigo-2); --bs-border-color: var(--line);
}
html { scroll-behavior: smooth; }
body { background: var(--paper); color: var(--ink); font-family: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif; -webkit-font-smoothing: antialiased; display: flex; flex-direction: column; min-height: 100vh; }
main { flex: 1 0 auto; }
a { color: var(--indigo); }
code { color: var(--ink-2); background: var(--paper-2); padding: .1em .35em; border-radius: 6px; font-size: .92em; }
.btn-primary { --bs-btn-bg: var(--indigo); --bs-btn-border-color: var(--indigo); --bs-btn-hover-bg: var(--indigo-2); --bs-btn-hover-border-color: var(--indigo-2); --bs-btn-active-bg: var(--indigo-2); font-weight: 650; border-radius: 10px; }
.btn-outline-primary { --bs-btn-color: var(--indigo); --bs-btn-border-color: var(--indigo); --bs-btn-hover-bg: var(--indigo); --bs-btn-hover-border-color: var(--indigo); border-radius: 10px; }

/* nav */
.mf-nav { background: rgba(251,250,247,.9); backdrop-filter: saturate(1.4) blur(8px); border-bottom: 1px solid var(--line); padding: .55rem 0; position: sticky; top: 0; z-index: 30; }
.mf-brand { font-weight: 800; letter-spacing: -.02em; color: var(--ink) !important; display: inline-flex; align-items: center; gap: .45rem; }
.mf-mark { display: inline-grid; place-items: center; width: 30px; height: 30px; border-radius: 9px; background: var(--indigo); color: #fff; font-weight: 700; font-size: 17px; }
.mf-nav .nav-link { color: var(--ink-2); font-weight: 560; }
.mf-nav .nav-link.active, .mf-nav .nav-link:hover { color: var(--ink); }
.navbar-toggler { border-color: var(--line); }
@media (max-width: 991px) { .mf-nav .navbar-nav { justify-content: center; flex-direction: row; flex-wrap: wrap; gap: .25rem 1rem; } .mf-nav-cta { margin-top: .25rem; } }

/* hero — centred, and centred hard (fleet rule) */
.mf-hero { text-align: center; padding: 3.5rem 0 2rem; background: radial-gradient(900px 340px at 50% -80px, var(--indigo-soft), transparent 70%); }
.mf-hero-sm { padding: 2.4rem 0 1.4rem; }
.mf-hero h1 { font-size: clamp(34px, 6.4vw, 68px); font-weight: 840; letter-spacing: -.038em; line-height: 1.02; margin: 0 auto .8rem; max-width: 900px; text-wrap: balance; }
.mf-hero-sm h1 { font-size: clamp(30px, 4.6vw, 48px); }
.mf-kicker-top { color: var(--indigo); font-weight: 700; letter-spacing: .02em; text-transform: uppercase; font-size: .78rem; margin: 0 auto .8rem; }
.mf-kicker-top a { text-decoration: none; }
.mf-sub { color: var(--ink-2); font-size: clamp(1.02rem, 1.4vw, 1.2rem); max-width: 720px; margin: 0 auto 1.6rem; text-wrap: balance; }
.mf-h1-icon { color: var(--indigo); }

/* solver */
.mf-solver { max-width: 860px; margin: 0 auto; }
.mf-inputrow { display: flex; gap: .5rem; background: #fff; border: 1.5px solid var(--line); border-radius: 16px; padding: .45rem; box-shadow: var(--shadow); transition: border-color .15s, box-shadow .15s; }
.mf-inputrow:focus-within { border-color: var(--indigo); box-shadow: 0 0 0 4px var(--indigo-soft); }
.mf-inputrow input { flex: 1; border: 0; outline: 0; background: transparent; font-size: 1.12rem; padding: .55rem .7rem; min-width: 0; font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; }
.mf-go { padding: .55rem 1.2rem; font-size: 1.02rem; white-space: nowrap; }
.mf-chips { display: flex; flex-wrap: wrap; justify-content: center; gap: .45rem; margin-top: .9rem; }
.mf-chip { font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; font-size: .86rem; color: var(--ink-2); background: #fff; border: 1px solid var(--line); border-radius: 999px; padding: .32rem .75rem; text-decoration: none; transition: all .12s; }
.mf-chip:hover { color: var(--indigo); border-color: var(--indigo); }

/* result */
.mf-out { max-width: 860px; margin: 1.6rem auto 0; text-align: left; }
.mf-out:empty { display: none; }
.mf-result { background: #fff; border: 1px solid var(--line); border-radius: var(--radius); box-shadow: var(--shadow); padding: 1.4rem 1.5rem 1.6rem; }
.mf-kicker { font-size: .78rem; text-transform: uppercase; letter-spacing: .04em; color: var(--ink-3); font-weight: 700; }
.mf-kicker a { color: var(--indigo); text-decoration: none; }
.mf-badge { background: var(--amber-soft); color: #8a5a0c; padding: .1em .55em; border-radius: 999px; text-transform: none; letter-spacing: 0; font-weight: 650; }
.mf-problem-title { font-size: 1.35rem; font-weight: 800; letter-spacing: -.02em; margin: .3rem 0 .5rem; }
.mf-display { font-size: 1.22rem; overflow-x: auto; padding: .35rem 0; }
.mf-display .katex-display { margin: .3rem 0; }
.mf-h3 { font-size: .86rem; text-transform: uppercase; letter-spacing: .05em; color: var(--ink-3); font-weight: 800; margin: 1.4rem 0 .5rem; }
.mf-steps { list-style: none; padding: 0; margin: 0; counter-reset: step; }
.mf-step { position: relative; padding: .8rem 1rem .8rem 3.1rem; border-left: 3px solid var(--line); margin: 0 0 .5rem; background: var(--paper); border-radius: 0 10px 10px 0; transition: opacity .35s, transform .35s, border-color .3s; }
.mf-step::before { counter-increment: step; content: counter(step); position: absolute; left: .85rem; top: .85rem; width: 1.55rem; height: 1.55rem; border-radius: 50%; background: var(--ink); color: #fff; font-size: .78rem; font-weight: 800; display: grid; place-items: center; }
.mf-step p { margin: .25rem 0 0; color: var(--ink-2); font-size: .97rem; }
.mf-step.is-hidden { display: none; }
.mf-step.is-new { animation: mf-in .45s ease-out both; border-left-color: var(--indigo); }
.mf-step.is-current { border-left-color: var(--indigo); background: var(--indigo-soft); }
@keyframes mf-in { from { opacity: 0; transform: translateY(8px); } to { opacity: 1; transform: none; } }
@media (prefers-reduced-motion: reduce) { .mf-step.is-new { animation: none; } html { scroll-behavior: auto; } }
.mf-controls { display: flex; flex-wrap: wrap; gap: .5rem; align-items: center; margin: .6rem 0 .2rem; }
.mf-controls .btn { border-radius: 10px; font-weight: 650; }
.mf-progress { color: var(--ink-3); font-size: .86rem; margin-left: auto; }
.mf-answer { margin-top: 1rem; border: 1.5px dashed var(--amber); background: var(--amber-soft); border-radius: 12px; padding: .7rem 1rem; }
.mf-answer summary, .mf-reveal { cursor: pointer; font-weight: 750; color: #8a5a0c; }
.mf-answer-body { padding-top: .4rem; }
.mf-answer-body .mf-display { font-size: 1.35rem; }
.mf-fail { background: #fdecea; border: 1px solid #f5c2bb; color: #7a2d20; border-radius: 12px; padding: .9rem 1rem; }
.mf-caveat { margin-top: .9rem; font-size: .9rem; color: var(--ink-2); border-left: 3px solid var(--amber); padding-left: .7rem; }
.mf-understood { font-style: italic; color: var(--ink-2); margin: .3rem 0 .6rem; }
.mf-parts { padding-left: 1.3rem; }
.mf-parts li { margin-bottom: .55rem; }
.mf-parts em { color: var(--ink-3); font-style: normal; }
.mf-approach { color: var(--ink-2); }
.mf-hints { list-style: none; padding: 0; margin: .3rem 0 0; }
.mf-hints li { margin-bottom: .35rem; }
.mf-hint-btn { background: none; border: 1px solid var(--line); border-radius: 999px; padding: .2rem .7rem; font-size: .88rem; color: var(--indigo); }
.mf-share { font-size: .85rem; color: var(--ink-3); margin-top: 1rem; }
.mf-share a { color: var(--ink-2); }
.mf-src { color: var(--ink-3); font-size: .78rem; }

/* visuals */
.mf-visual { margin-top: 1.1rem; border: 1px solid var(--line); border-radius: 12px; background: var(--paper); overflow: hidden; }
.mf-visual canvas, .mf-visual svg { display: block; width: 100%; height: auto; }
.mf-visual-cap { font-size: .82rem; color: var(--ink-3); padding: .4rem .8rem; border-top: 1px solid var(--line); display: flex; justify-content: space-between; gap: 1rem; flex-wrap: wrap; }
.mf-visual-cap .mf-legend span { display: inline-flex; align-items: center; gap: .3rem; margin-right: .8rem; }
.mf-visual-cap .mf-legend i { display: inline-block; width: 14px; height: 3px; border-radius: 2px; }
.mf-table { width: 100%; border-collapse: collapse; font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; font-size: .95rem; }
.mf-table th, .mf-table td { border-bottom: 1px solid var(--line); padding: .35rem .7rem; text-align: center; }
.mf-table th { background: var(--paper-2); }
.mf-table td.T { color: var(--green); font-weight: 700; } .mf-table td.F { color: var(--red); font-weight: 700; }

/* sections + cards */
.mf-h2 { font-size: clamp(1.4rem, 2.6vw, 1.9rem); font-weight: 820; letter-spacing: -.03em; margin: 0 0 .4rem; }
.mf-section-sub { color: var(--ink-2); margin-bottom: 1.4rem; }
.mf-branches { padding: 2.6rem 0 1rem; }
.mf-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(230px, 1fr)); gap: .9rem; }
.mf-card { display: flex; flex-direction: column; gap: .25rem; background: #fff; border: 1px solid var(--line); border-radius: var(--radius); padding: 1.1rem 1.15rem; text-decoration: none; color: var(--ink); box-shadow: var(--shadow); transition: transform .15s, border-color .15s; }
.mf-card:hover { transform: translateY(-2px); border-color: var(--indigo); color: var(--ink); }
.mf-card-icon { font-size: 1.7rem; color: var(--indigo); line-height: 1; margin-bottom: .3rem; }
.mf-card-name { font-weight: 780; font-size: 1.08rem; letter-spacing: -.015em; }
.mf-card-tag { color: var(--ink-2); font-size: .92rem; }
.mf-card-count, .mf-card-level { color: var(--ink-3); font-size: .78rem; text-transform: uppercase; letter-spacing: .04em; font-weight: 700; }
.mf-card-ex { margin-top: .4rem; align-self: flex-start; font-size: .82rem; }
.mf-inline-links a { display: inline-block; margin: 0 .8rem .5rem 0; text-decoration: none; font-weight: 600; }
.mf-how { padding: 2rem 0 3rem; }
.mf-how-grid { margin-top: 1.2rem; }
.mf-how-item h3 { font-size: 1.05rem; font-weight: 780; letter-spacing: -.015em; margin: .5rem 0 .3rem; }
.mf-how-item p { color: var(--ink-2); font-size: .95rem; }
.mf-how-n { display: inline-grid; place-items: center; width: 30px; height: 30px; border-radius: 50%; background: var(--ink); color: #fff; font-weight: 800; font-size: .85rem; }

/* prose */
.mf-prose { font-size: 1.05rem; line-height: 1.65; max-width: 760px; }
.mf-prose p { margin-bottom: 1rem; }
.mf-narrow { max-width: 760px; padding-bottom: 3rem; }
.mf-topic-body { padding: 1rem 0 3rem; max-width: 900px; }
.mf-topic-body .mf-h2 { margin-top: 2rem; }
.mf-topic-body .mf-out { margin-left: 0; }

/* footer */
.mf-footer { border-top: 1px solid var(--line); padding: 1.6rem 0 2rem; margin-top: 2rem; color: var(--ink-3); font-size: .92rem; }
.mf-footer-links a { margin: 0 .6rem; text-decoration: none; color: var(--ink-2); }

/* legal + misc pages keep bootstrap layout; give them air */
.page-terms main, .page-privacy main, .page-contact main, .page-login main, .page-register main, .page-account main { padding: 1.5rem 0; }

/* learning path — the above-the-fold thing */
.mf-path-hero { text-align: center; padding: 2rem 0 1.2rem; background: radial-gradient(900px 340px at 50% -80px, var(--indigo-soft), transparent 70%); }
.mf-path-hero h1 { font-size: clamp(30px, 4.8vw, 52px); font-weight: 840; letter-spacing: -.038em; line-height: 1.02; margin: 0 auto .5rem; max-width: 900px; text-wrap: balance; }
.mf-path-hero .mf-sub { margin-bottom: 1.2rem; }
.mf-path { list-style: none; padding: 0; margin: 0 auto; display: grid; grid-template-columns: repeat(auto-fit, minmax(118px, 1fr)); gap: .55rem; max-width: 1180px; counter-reset: stage; }
.mf-path-card { display: flex; flex-direction: column; align-items: center; gap: .15rem; background: #fff; border: 1.5px solid var(--line); border-radius: 14px; padding: .8rem .4rem .7rem; text-decoration: none; color: var(--ink); box-shadow: var(--shadow); position: relative; transition: transform .15s, border-color .15s; min-height: 118px; justify-content: center; }
.mf-path-card:hover { transform: translateY(-2px); border-color: var(--indigo); color: var(--ink); }
.mf-path-card.is-frontier { border-style: dashed; border-color: var(--amber); }
.mf-path-n { position: absolute; top: 6px; left: 8px; font-size: .7rem; font-weight: 800; color: var(--ink-3); }
.mf-path-icon { font-size: 1.5rem; color: var(--indigo); line-height: 1; }
.mf-path-name { font-weight: 760; font-size: .86rem; letter-spacing: -.01em; line-height: 1.15; }
.mf-path-count { font-size: .68rem; color: var(--ink-3); text-transform: uppercase; letter-spacing: .04em; font-weight: 700; }
.mf-card-icon-inline { color: var(--indigo); }
@media (max-width: 600px) { .mf-path { grid-template-columns: repeat(3, 1fr); gap: .45rem; } .mf-path-card { min-height: 100px; padding: .7rem .3rem .6rem; } .mf-path-hero { padding-top: 1.4rem; } }

/* draw pad + keypad */
.mf-modes { display: flex; justify-content: center; gap: .4rem; margin-bottom: .5rem; }
.mf-mode { background: #fff; border: 1px solid var(--line); border-radius: 999px; padding: .28rem .9rem; font-weight: 650; color: var(--ink-2); font-size: .9rem; }
.mf-mode.is-on { background: var(--ink); color: #fff; border-color: var(--ink); }
.mf-pad { background: #fff; border: 1.5px solid var(--line); border-radius: 16px; box-shadow: var(--shadow); overflow: hidden; }
.mf-pad[hidden] { display: none; }
.mf-pad canvas { display: block; width: 100%; height: 220px; touch-action: none; cursor: crosshair; background: repeating-linear-gradient(0deg, transparent, transparent 27px, #f1efe8 27px, #f1efe8 28px); }
.mf-pad-bar { display: flex; gap: .4rem; align-items: center; padding: .5rem .6rem; border-top: 1px solid var(--line); flex-wrap: wrap; }
.mf-pad-bar .btn { border-radius: 10px; font-weight: 650; }
.mf-pad-hint { font-size: .82rem; color: var(--ink-3); margin-left: auto; }
.mf-keys { display: flex; flex-wrap: wrap; justify-content: center; gap: .3rem; margin-top: .55rem; }
.mf-key { font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; font-size: .9rem; background: #fff; border: 1px solid var(--line); border-radius: 8px; padding: .25rem .55rem; color: var(--ink); min-width: 2.2rem; }
.mf-key:hover { border-color: var(--indigo); color: var(--indigo); }
.mf-recognised { font-size: .9rem; color: var(--ink-2); padding: .4rem .6rem; }

/* tutorial sections + practice bank */
.mf-section { margin: 1.2rem 0 1.6rem; }
.mf-section h3 { font-size: 1.15rem; font-weight: 800; letter-spacing: -.02em; margin: 0 0 .5rem; }
.mf-section .mf-prose p { margin-bottom: .8rem; }
.mf-section .mf-example { background: var(--paper-2); border-left: 3px solid var(--indigo); border-radius: 0 10px 10px 0; padding: .7rem 1rem; margin: .8rem 0; }
.mf-section .mf-example summary { font-weight: 700; cursor: pointer; }
.mf-attrib { font-size: .8rem; color: var(--ink-3); border-top: 1px solid var(--line); padding-top: .5rem; margin-top: 1.5rem; }
.mf-practice { list-style: none; padding: 0; margin: 0; counter-reset: ex; }
.mf-practice li { position: relative; padding: .6rem .8rem .6rem 2.6rem; border: 1px solid var(--line); border-radius: 10px; margin-bottom: .5rem; background: #fff; }
.mf-practice li::before { counter-increment: ex; content: counter(ex); position: absolute; left: .75rem; top: .7rem; width: 1.35rem; height: 1.35rem; border-radius: 50%; background: var(--paper-2); color: var(--ink-2); font-size: .74rem; font-weight: 800; display: grid; place-items: center; }
.mf-practice .mf-ex-actions { margin-top: .3rem; display: flex; gap: .6rem; flex-wrap: wrap; font-size: .85rem; }
.mf-practice .mf-verified { color: var(--green); font-weight: 700; font-size: .78rem; }
.mf-toc { display: flex; flex-wrap: wrap; gap: .4rem; margin: .6rem 0 1rem; }
.mf-toc a { font-size: .84rem; text-decoration: none; background: #fff; border: 1px solid var(--line); border-radius: 999px; padding: .22rem .7rem; color: var(--ink-2); }