:root {
  --ink: #152347; --muted: #53607a; --blue: #233cc7; --blue-dark: #182993;
  --yellow: #e4f75b; --paper: #f5f7fc; --line: #dce1ed; --green: #16684b;
  --orange: #ac4818; --purple: #6941ac; --error: #a12b31;
  font-family: "Segoe UI", system-ui, sans-serif; color: var(--ink); background: var(--paper);
  font-synthesis: none; line-height: 1.55;
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 24px; }
body { margin: 0; }
a { color: var(--blue); text-underline-offset: 4px; }
button, input, select { font: inherit; }
button, .button { cursor: pointer; }
button, .button { display: inline-flex; align-items: center; justify-content: center; gap: 12px; padding: 13px 21px; min-height: 48px; border-radius: 8px; border: 1px solid transparent; font-weight: 650; text-decoration: none; line-height: 1.3; transition: background .18s, box-shadow .18s, transform .18s; }
.primary { background: var(--blue); color: white; }
.primary:hover { background: var(--blue-dark); box-shadow: 0 5px 12px #14247726; }
.secondary { color: var(--ink); background: white; border-color: #adb8d0; }
.secondary:hover { background: #eaf0ff; }
.yellow { background: var(--yellow); color: var(--ink); }
.yellow:hover { background: #f2ff8d; transform: translateY(-2px); }
.danger { background: white; color: var(--error); border-color: #b44950; }
.danger:hover { background: #fff0f1; }
:focus-visible { outline: 3px solid var(--orange); outline-offset: 4px; }
button:disabled { opacity: .55; cursor: default; transform: none; box-shadow: none; }
h1, h2, h3, p { margin: 0; }
h1 { font-size: clamp(2.5rem, 5.2vw, 4.6rem); line-height: 1.06; letter-spacing: -.035em; font-weight: 750; text-wrap: balance; }
h2 { font-size: clamp(1.7rem, 3vw, 2.4rem); line-height: 1.18; letter-spacing: -.025em; text-wrap: balance; }
h3 { font-size: 1.15rem; line-height: 1.35; }
p { margin-top: 14px; max-width: 70ch; }
.lead { font-size: 1.18rem; color: var(--muted); line-height: 1.65; }
.about a { overflow-wrap: anywhere; }
small, .fine-print { font-size: .83rem; color: var(--muted); }
.topbar { max-width: 1392px; margin: auto; display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 24px; padding: 23px 48px; border-bottom: 1px solid var(--line); }
.brand { display: flex; gap: 10px; align-items: center; font-size: 1.18rem; font-weight: 750; text-decoration: none; color: var(--ink); white-space: nowrap; }
.brand-mark { width: 35px; height: 35px; border-radius: 9px 3px 9px 3px; background: var(--blue); color: var(--yellow); display: grid; place-items: center; font-size: 1.7rem; font-family: Georgia, serif; font-style: italic; }
.course-label { margin-left: 12px; font-size: .8rem; font-weight: 500; color: var(--muted); border-left: 1px solid #c1cadd; padding-left: 20px; }
.course-switcher { display: flex; align-items: center; flex-wrap: wrap; gap: 12px 20px; max-width: 1296px; margin: auto; padding: 18px 48px 0; font-size: .88rem; }
.course-switcher label { font-weight: 650; }
.course-switcher select { max-width: 100%; min-height: 44px; color: var(--ink); background: white; border: 1px solid #8797b6; border-radius: 6px; padding: 9px 12px; font: inherit; }
.course-switcher a { margin-left: auto; }
.course-catalog { padding: 0; list-style: none; }
.course-catalog li { display: flex; align-items: center; gap: 35px; justify-content: space-between; padding: 32px 0; border-bottom: 1px solid var(--line); }
.course-catalog h2 { font-size: 1.85rem; }
.course-catalog li p { max-width: 65ch; color: var(--muted); }
.course-catalog li span { display: block; margin-top: 14px; font-size: .85rem; }
.course-catalog li .button { flex-shrink: 0; }
.subject-interactive { align-self: start; }
.subject-interactive fieldset { border: 0; padding: 0; margin: 20px 0; }
.subject-interactive legend { font-weight: 650; font-size: .95rem; margin-bottom: 12px; }
.subject-interactive label { display: block; margin-top: 16px; font-size: .9rem; }
.subject-interactive .answer { display: flex; margin-top: 8px; }
.subject-interactive input[type=range], .subject-interactive select { display: block; width: 100%; margin-top: 8px; }
.subject-interactive select { padding: 10px; font: inherit; color: var(--ink); background: white; }
.course-model { width: 100%; height: auto; display: block; margin-top: 16px; background: #eef2ff; border-radius: 6px; }
nav { display: flex; gap: 8px; }
nav a { color: var(--muted); font-size: .9rem; text-decoration: none; padding: 10px 13px; border-radius: 6px; }
nav a:hover { color: var(--blue); background: #e9eeff; }
nav a[aria-current] { background: var(--blue); color: white; }
main { max-width: 1296px; margin: auto; padding: 44px 48px 72px; min-height: 70vh; }
main:focus { outline: none; }
.skip { position: absolute; left: 15px; top: -100px; background: white; z-index: 10; padding: 12px; }
.skip:focus { top: 12px; }
.welcome { display: grid; grid-template-columns: 1.1fr 1fr; gap: 72px; align-items: center; padding: 12px 0 36px; }
.welcome-copy h1 { font-size: clamp(3rem, 5.5vw, 5rem); }
.welcome-copy h1 span { color: var(--blue); }
.welcome-copy .lead { margin-top: 26px; max-width: 41ch; }
.onboarding-note { margin-top: 32px; font-size: .95rem; }
.text-link { display: inline-block; font-weight: 650; margin-top: 14px; }
.welcome-lab { background: var(--yellow); padding: 20px; border-radius: 18px 18px 72px 18px; }
.experiment { background: white; border-radius: 12px; padding: 23px; border: 1px solid var(--line); }
.experiment-head { display: flex; justify-content: space-between; gap: 12px; align-items: center; }
.experiment-head h3 { font-size: 1.03rem; }
.live-dot { display: inline-flex; align-items: center; gap: 6px; font-size: .7rem; color: var(--green); white-space: nowrap; }
.live-dot::before { content: ""; height: 6px; width: 6px; border-radius: 50%; background: var(--green); }
.plot { display: block; width: 100%; max-height: 355px; aspect-ratio: 1; overflow: hidden; }
.plot text { font-family: "Segoe UI", sans-serif; font-size: 11px; fill: var(--muted); }
.gridline { fill: none; stroke: #e7ebf3; stroke-width: 1; }
.axis { fill: none; stroke: #9aa8c1; stroke-width: 1.5; }
.curve { fill: none; stroke: var(--blue); stroke-width: 3; stroke-linecap: round; stroke-linejoin: round; }
.asymptote { fill: none; stroke: var(--orange); stroke-width: 1.6; stroke-dasharray: 5 5; }
.inverse { fill: none; stroke: var(--orange); stroke-width: 2.5; stroke-dasharray: 7 4; }
.diagonal { fill: none; stroke: #677696; stroke-width: 1.4; stroke-dasharray: 2 5; }
.projection { fill: none; stroke: var(--orange); stroke-width: 1.8; stroke-dasharray: 4 3; }
.radius { fill: none; stroke: var(--ink); stroke-width: 2; }
.point { fill: var(--orange); stroke: white; stroke-width: 2; }
.controls { display: grid; grid-template-columns: repeat(2, 1fr); gap: 12px 18px; }
.controls label { display: grid; grid-template-columns: 1fr auto; font-size: .8rem; align-items: center; gap: 4px; }
.controls input, .controls select { grid-column: 1 / -1; min-width: 0; width: 100%; }
.controls select { padding: 8px; border-radius: 4px; color: var(--ink); border: 1px solid #98a5bd; background: white; }
input[type=range] { accent-color: var(--blue); cursor: ew-resize; height: 24px; margin: 0; }
.controls output { font-variant-numeric: tabular-nums; font-weight: 700; }
.math-readout { padding: 12px; background: #eef2ff; border-radius: 6px; margin-top: 16px; font-size: .85rem; min-height: 65px; }
.experiment-prompt { font-size: .9rem; }
.experiment small { display: block; margin-top: 12px; font-size: .73rem; }
.welcome .experiment-prompt, .welcome .experiment small { display: none; }
.welcome .plot { max-height: 260px; }
.program-section { margin-top: 34px; border-top: 1px solid var(--line); padding-top: 35px; }
.program-choices { border: 0; padding: 0; margin: 26px 0 22px; display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px; }
.program-choices legend { padding: 0; margin-bottom: 13px; font-weight: 650; }
.program-choice { display: grid; grid-template-columns: 1fr auto; position: relative; border: 1px solid #abb7ce; border-radius: 10px; background: white; padding: 20px 23px; cursor: pointer; transition: border-color .2s, background .2s; }
.program-choice:has(:checked) { border: 2px solid var(--blue); padding: 19px 22px; background: #edf1ff; }
.program-choice:hover { border-color: var(--blue); }
.program-choice input { grid-column: 2; grid-row: 1; accent-color: var(--blue); width: 19px; height: 19px; }
.program-choice > span, .program-choice > strong, .program-choice > small { grid-column: 1 / -1; }
.program-choice .program-months { grid-column: 1; font-size: 2.2rem; font-weight: 750; line-height: 1.2; margin-bottom: 15px; }
.program-months span { font-size: .94rem; font-weight: 500; }
.program-choice > strong { font-size: 1rem; }
.program-choice > span:not(.program-months) { font-size: .87rem; margin-top: 8px; }
.program-choice small { margin-top: 3px; }
.program-submit { display: flex; align-items: center; gap: 23px; }
.program-submit > span { font-size: .86rem; color: var(--muted); }
.fine-print { margin-top: 20px; }
footer { border-top: 1px solid var(--line); max-width: 1200px; margin: auto; padding: 24px 48px 34px; display: flex; gap: 16px; justify-content: space-between; flex-wrap: wrap; font-size: .78rem; color: var(--muted); }
footer > span:last-child { width: 100%; font-size: .72rem; }
.dashboard-intro { display: flex; justify-content: space-between; align-items: center; gap: 28px; margin: 8px 0 35px; }
.dashboard-intro h1 { font-size: clamp(2.3rem, 4.1vw, 3.7rem); }
.dashboard-intro .button { flex-shrink: 0; }
.study-workspace { display: grid; grid-template-columns: 1.15fr 1fr; background: var(--blue); border-radius: 18px; overflow: hidden; }
.next-up { color: white; padding: 44px; display: flex; flex-direction: column; align-items: flex-start; justify-content: center; }
.next-status { font-size: .83rem; margin-bottom: 27px; color: #edf0ff; }
.next-status span { display: block; color: #cbd5ff; margin-top: 5px; }
.next-up h2 { font-size: clamp(2rem, 3.4vw, 3.1rem); }
.next-up p { color: #e0e6ff; }
.lesson-meta { display: flex; flex-wrap: wrap; gap: 8px 17px; color: var(--muted); font-size: .82rem; margin-top: 23px; }
.next-up .lesson-meta { color: #e0e6ff; margin-bottom: 25px; }
.next-up .study-tip { font-size: .8rem; margin-top: 23px; }
.dashboard-graph { padding: 24px; background: #e4eaff; }
.dashboard-graph .experiment { border: none; }
.progress-strip { display: flex; justify-content: space-between; align-items: center; gap: 30px; padding: 30px 0; border-bottom: 1px solid var(--line); }
.progress-strip strong, .progress-strip span { display: block; }
.progress-strip span { font-size: .83rem; margin-top: 5px; color: var(--muted); }
progress { width: 240px; height: 10px; accent-color: var(--blue); border: none; border-radius: 5px; background: #dce2f3; flex-shrink: 0; }
progress::-webkit-progress-bar { background: #dce2f3; border-radius: 5px; }
progress::-webkit-progress-value { background: var(--blue); border-radius: 5px; }
.week-preview { padding: 40px 0; display: grid; grid-template-columns: 1fr 1fr; gap: 20px 50px; border-bottom: 1px solid var(--line); }
.week-preview > .button { justify-self: start; }
.weekly-links { display: flex; flex-direction: column; align-items: flex-start; gap: 9px; }
.weekly-links h3:not(:first-child) { margin-top: 16px; }
.weekly-links a { font-size: .94rem; }
.course-map-intro { margin-top: 44px; }
.unit-overview { margin-top: 27px; display: flex; flex-direction: column; }
.unit-overview-item { display: flex; gap: 25px; padding: 24px 0; text-decoration: none; color: var(--ink); border-bottom: 1px solid var(--line); }
.unit-overview-item:hover h3 { color: var(--blue); }
.unit-number { display: grid; place-items: center; width: 45px; height: 45px; background: #dfe6ff; color: var(--blue); border-radius: 50%; flex-shrink: 0; font-size: 1.2rem; font-weight: 750; }
.orange .unit-number { background: #ffe3cd; color: var(--orange); }
.purple .unit-number { background: #ece1ff; color: var(--purple); }
.unit-overview-item p { margin-top: 5px; color: var(--muted); }
.unit-overview-item .text-link { margin-top: 6px; color: var(--blue); font-size: .84rem; }
.page-heading { margin: 12px 0 34px; }
.page-heading > p { max-width: 65ch; }
.page-heading h1 { max-width: 20ch; }
.unit-block { background: white; margin-bottom: 22px; border: 1px solid var(--line); border-radius: 10px; overflow: hidden; }
summary { cursor: pointer; }
.unit-block summary { padding: 22px 25px; font-size: 1.3rem; font-weight: 700; background: #e9eeff; }
.unit-block.orange summary { background: #ffecd9; }
.unit-block.purple summary { background: #eee6ff; }
.unit-block.green summary { background: #e3f4eb; }
.unit-completion { float: right; font-weight: 500; font-size: .85rem; margin-top: 5px; }
.unit-description { padding: 6px 25px 19px; color: var(--muted); font-size: .9rem; }
.unit-description > span { font-size: .8rem; display: block; margin-top: 6px; }
.unit-checkpoint { border-top: 1px solid var(--line); padding: 24px 25px; display: flex; align-items: center; justify-content: space-between; gap: 24px; background: #f5f7ff; }
.unit-checkpoint p { font-size: .9rem; margin-top: 7px; }
.unit-checkpoint span { display: block; color: var(--muted); font-size: .8rem; margin-top: 9px; }
.unit-checkpoint .button { flex-shrink: 0; }
.unit-progress { padding: 26px 0; border-bottom: 1px solid var(--line); }
.unit-progress > p { color: var(--muted); font-size: .85rem; }
.unit-progress > a { display: flex; justify-content: space-between; gap: 18px; padding-top: 14px; font-size: .9rem; }
.unit-progress > a span { color: var(--muted); font-size: .8rem; }
.checkpoint-topics { margin-top: 40px; }
.checkpoint-topics h2 { font-size: 1.5rem; margin-bottom: 16px; }
.checkpoint-topics a { display: block; margin-top: 9px; }
.test-toolbar { display: flex; justify-content: space-between; gap: 18px; align-items: center; background: var(--paper); position: sticky; top: 0; z-index: 2; padding: 16px 0; border-bottom: 1px solid var(--line); }
.test-toolbar h2 { font-size: 1.45rem; }
.test-toolbar span { display: block; margin-top: 6px; font-size: .85rem; }
.test-instructions { margin: 22px 0; font-size: .95rem; }
.question-jumps { display: flex; flex-wrap: wrap; gap: 8px; margin: 25px 0 35px; }
.question-jumps a { min-width: 42px; height: 42px; display: grid; place-items: center; padding: 6px; border: 1px solid #adb8d0; background: white; border-radius: 5px; color: var(--blue); }
.question-jumps a.answered { color: white; background: var(--blue); border-color: var(--blue); }
.test-navigator { margin: 22px 0 32px; border-bottom: 1px solid var(--line); padding-bottom: 16px; }
.test-navigator summary { color: var(--blue); font-weight: 650; font-size: .9rem; }
.test-navigator .question-jumps { margin: 18px 0 0; }
.question-context { margin: -4px 0 14px 44px; font-size: .8rem; color: var(--muted); }
#unit-test-form .question, #subject-quiz-form .question { scroll-margin-top: 125px; }
.topic-feedback-heading { margin-top: 25px; }
.topic-feedback { list-style: none; padding: 0; margin: 12px 0; }
.topic-feedback li { display: flex; justify-content: space-between; gap: 18px; padding: 10px 0; border-bottom: 1px solid #c3cde1; font-size: .9rem; }
.topic-feedback li span { font-size: .8rem; color: var(--muted); }
.practice-entry { display: flex; justify-content: space-between; align-items: center; gap: 30px; padding: 32px 0; border-bottom: 1px solid var(--line); }
.practice-entry h2 { font-size: 1.8rem; }
.practice-entry p { font-size: .95rem; color: var(--muted); }
.practice-entry strong { display: block; margin-top: 12px; font-size: .9rem; }
.practice-entry .button { flex-shrink: 0; }
.practice-round-list { list-style: none; margin: 25px 0 0; padding: 0; }
.practice-round-list > li { display: flex; align-items: center; gap: 20px; padding: 24px 0; border-bottom: 1px solid var(--line); }
.round-number { width: 40px; height: 40px; flex-shrink: 0; display: grid; place-items: center; background: #e5eaff; color: var(--blue); border-radius: 50%; font-weight: 700; }
.round-earned .round-number { color: var(--green); background: #ddf4e8; }
.practice-round-list h2 { font-size: 1.24rem; }
.practice-round-list p { margin-top: 6px; font-size: .9rem; color: var(--muted); }
.practice-round-list div > span { display: block; margin-top: 7px; font-size: .82rem; }
.practice-round-list .button, .round-lock { margin-left: auto; flex-shrink: 0; }
.round-lock { color: var(--muted); font-size: .85rem; }
.practice-heading { max-width: 900px; }
.practice-guide { margin-top: 22px; max-width: 700px; }
.practice-guide summary { color: var(--blue); font-size: .95rem; font-weight: 650; }
.qa-slot { margin: 28px 0; }
[data-open-qa] { margin-top: 18px; }
.qa-panel { border: 1px solid #adb8d0; background: white; border-radius: 8px; }
.qa-panel > summary { padding: 18px 22px; cursor: pointer; color: var(--blue); font-weight: 650; }
.qa-panel > summary span { margin-left: 15px; font-size: .8rem; color: var(--muted); font-weight: 500; }
.qa-body { padding: 8px 24px 26px; max-width: 950px; }
.qa-body h2 { font-size: 1.65rem; }
.qa-context { color: var(--blue); font-size: .92rem; font-weight: 650; }
.qa-privacy { font-size: .86rem; color: var(--muted); }
.qa-suggestions, .qa-choices, .qa-all-questions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 20px; }
.qa-suggestions button, .qa-choices button, .qa-all-questions button { padding: 10px 13px; min-height: 44px; text-align: left; font-size: .86rem; justify-content: flex-start; }
.qa-library { margin-top: 18px; }
.qa-library summary { cursor: pointer; color: var(--blue); font-size: .9rem; }
.qa-history { list-style: none; padding: 0; margin: 24px 0; max-height: 560px; overflow-y: auto; overscroll-behavior: contain; }
.qa-history:empty { display: none; }
.qa-history li + li { margin-top: 24px; }
.qa-student { background: #edf1ff; padding: 14px 18px; border-radius: 6px; }
.qa-student p, .qa-backlog-list article > p { white-space: pre-wrap; overflow-wrap: anywhere; }
.qa-student p { margin-top: 5px; }
.qa-student small { display: block; margin-top: 8px; }
.qa-response { padding: 16px 18px; border-bottom: 1px solid var(--line); font-size: .95rem; overflow-wrap: anywhere; }
.qa-response p { margin-top: 10px; }
.qa-response button { margin-top: 16px; }
.qa-form > label { display: block; font-weight: 650; }
.qa-form { margin-top: 20px; }
.qa-input { display: block; margin-top: 8px; width: 100%; max-width: 700px; min-height: 80px; resize: vertical; border: 1px solid #8797b6; border-radius: 6px; padding: 12px; font: inherit; color: var(--ink); background: white; }
.qa-form .result-actions { margin-top: 15px; }
.qa-error, .qa-backlog-error, .qa-delete-error { color: var(--error); }
.qa-backlog-list { margin-top: 32px; }
.qa-backlog-list h2 { font-size: 1.6rem; }
.qa-backlog-list article { border-bottom: 1px solid var(--line); padding: 26px 0; }
.qa-backlog-list article button { margin-top: 18px; }
.practice-heading h1 { font-size: clamp(2.3rem, 4.4vw, 3.8rem); }
.practice-levels { display: grid; grid-template-columns: repeat(3, 1fr); list-style: none; padding: 0; margin: 30px 0 15px; border: 1px solid #c3cde1; border-radius: 8px; overflow: hidden; }
.practice-levels li { padding: 17px 20px; background: #edf1ff; }
.practice-levels li + li { border-left: 1px solid #c3cde1; }
.practice-levels .locked { background: #edf0f5; color: var(--muted); }
.practice-levels span { display: block; font-size: .8rem; margin-top: 5px; }
.practice-support { font-size: .85rem; color: var(--muted); margin-bottom: 26px; }
.practice-question { max-width: 880px; border: 1px solid var(--line); border-radius: 10px; background: white; padding: 30px; }
.practice-question-meta { display: flex; justify-content: space-between; gap: 14px; font-size: .86rem; color: var(--muted); }
.practice-question-meta strong { color: var(--blue); }
.practice-question h2 { margin-top: 22px; font-size: clamp(1.25rem, 2.6vw, 1.7rem); line-height: 1.4; scroll-margin-top: 25px; }
#practice-answer-form { margin-top: 24px; }
#practice-answer-form > label { display: block; font-weight: 650; font-size: .95rem; }
#practice-answer { display: block; border: 1px solid #8797b6; border-radius: 6px; margin-top: 8px; padding: 12px 14px; width: 100%; max-width: 340px; color: var(--ink); background: white; }
#practice-answer-error { color: var(--error); font-size: .9rem; }
.practice-hint { background: #fff4df; border-radius: 6px; padding: 18px; margin-top: 22px; color: #683d0b; }
.practice-hint p { margin-top: 6px; font-size: .94rem; }
.practice-feedback { border-top: 1px solid var(--line); padding-top: 24px; margin-top: 26px; }
.practice-feedback.correct h3 { color: var(--green); }
.practice-feedback.incorrect > strong { color: var(--error); }
.practice-feedback p { font-size: .95rem; }
.practice-feedback .button, .practice-feedback button { margin-top: 20px; }
.practice-review { margin-top: 30px; max-width: 880px; }
.practice-review summary { color: var(--blue); font-weight: 650; }
.practice-review article { margin-top: 20px; padding: 20px 0; border-bottom: 1px solid var(--line); }
.practice-review h3 { font-size: 1rem; line-height: 1.6; }
.practice-review small { display: block; margin-top: 9px; }
.lesson-list { list-style: none; padding: 0; margin: 0; }
.lesson-list li { border-top: 1px solid var(--line); }
.lesson-list a { display: flex; gap: 15px; align-items: center; padding: 20px 25px; color: var(--ink); text-decoration: none; }
.lesson-list a:hover { background: #f5f7ff; }
.lesson-state { color: var(--muted); background: #f0f3fa; border-radius: 50%; min-width: 30px; height: 30px; display: grid; place-items: center; }
.lesson-state.complete { color: var(--green); background: #ddf4e8; }
.lesson-list strong { font-size: .99rem; }
.lesson-list div > span { display: block; font-size: .86rem; color: var(--muted); margin-top: 4px; }
.list-meta { margin-left: auto; text-align: right; flex-shrink: 0; font-size: .8rem; }
.list-meta small { display: block; margin-top: 4px; font-size: .73rem; }
.planner-key { padding: 20px 0; display: flex; align-items: center; gap: 20px; border-bottom: 1px solid var(--line); margin-bottom: 24px; }
.planner-key .button { margin-left: auto; }
.planner-key > span { font-size: .9rem; }
.week { border-bottom: 1px solid var(--line); }
.week summary { padding: 20px 4px; display: flex; align-items: center; gap: 35px; }
.week summary::before { content: "+"; color: var(--blue); font-size: 1.3rem; }
.week[open] summary::before { content: "−"; }
.week summary > span:first-of-type { min-width: 72px; }
.week summary strong { font-size: .99rem; }
.week-status { margin-left: auto; color: var(--muted); font-size: .8rem; }
.week-content { padding: 0 18px 27px 60px; }
.week-content > p { margin-top: 0; font-size: .92rem; }
.week-columns { display: grid; grid-template-columns: repeat(3, 1fr); gap: 28px; margin-top: 23px; }
.week-columns a { display: block; margin-top: 10px; font-size: .9rem; }
.week-columns p { font-size: .8rem; color: var(--muted); }
.lesson-breadcrumb { display: flex; justify-content: space-between; gap: 16px; font-size: .85rem; color: var(--muted); margin-bottom: 26px; }
.lesson-heading { max-width: 900px; margin-bottom: 38px; }
.lesson-heading h1 { font-size: clamp(2.5rem, 4.4vw, 4rem); }
.lesson-workspace { display: grid; grid-template-columns: 1.15fr 1fr; align-items: start; gap: 55px; }
.lesson-reading h2 { font-size: 1.5rem; }
.lesson-reading > p { font-size: 1.02rem; line-height: 1.8; margin-top: 20px; }
.worked-example { background: #e9eeff; padding: 23px; border-radius: 8px; margin-top: 30px; }
.worked-example p { font-size: .96rem; line-height: 1.75; }
.watch-for { margin: 26px 0; padding: 0 0 22px; border-bottom: 1px solid var(--line); }
.watch-for strong { color: var(--orange); }
.watch-for p { margin-top: 6px; font-size: .93rem; }
.lesson-experiment { position: sticky; top: 24px; }
.quiz-section { margin-top: 70px; padding-top: 38px; border-top: 2px solid var(--ink); }
.quiz-heading { display: flex; justify-content: space-between; align-items: center; gap: 20px; margin-bottom: 30px; }
.quiz-heading p { font-size: .95rem; color: var(--muted); }
.quiz-count { white-space: nowrap; font-size: .87rem; }
.question { border: 0; border-bottom: 1px solid var(--line); padding: 0 0 26px; margin: 0 0 30px; min-width: 0; }
.question legend { padding: 0; display: flex; gap: 14px; align-items: flex-start; font-size: 1.07rem; font-weight: 650; margin-bottom: 18px; max-width: 75ch; }
.question-number { color: var(--blue); background: #e3e9ff; min-width: 30px; height: 30px; border-radius: 5px; display: grid; place-items: center; font-size: .88rem; flex-shrink: 0; }
.answers { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; max-width: 930px; }
.answer { display: flex; align-items: center; gap: 12px; cursor: pointer; border: 1px solid #afb9cf; background: white; border-radius: 7px; padding: 13px 16px; font-size: .94rem; min-height: 51px; }
.answer input { accent-color: var(--blue); width: 18px; height: 18px; flex-shrink: 0; margin: 0; }
.answer:hover { border-color: var(--blue); }
.answer:has(:checked) { background: #e9eeff; border-color: var(--blue); }
.answer.answer-correct { background: #e5f5ed; border-color: var(--green); }
.answer.answer-wrong { background: #fff0f1; border-color: var(--error); }
.explanation { margin-top: 17px; font-size: .9rem; max-width: 80ch; }
.explanation p { margin-top: 6px; }
.explanation.correct > strong { color: var(--green); }
.explanation.incorrect > strong { color: var(--error); }
.quiz-actions { display: flex; align-items: center; gap: 20px; }
#quiz-error { color: var(--error); margin: 0; }
.quiz-result { margin-top: 28px; border-radius: 10px; background: #e8edf9; padding: 25px; }
.quiz-result h3 { font-size: 1.5rem; }
.result-actions { display: flex; flex-wrap: wrap; gap: 12px; margin-top: 23px; }
.lesson-bottom { display: flex; justify-content: space-between; gap: 20px; margin-top: 40px; }
.device-settings { margin-top: 50px; padding-top: 32px; border-top: 1px solid var(--line); }
.backup-controls { display: flex; flex-wrap: wrap; gap: 12px; margin-top: 22px; }
.visually-hidden { position: absolute; width: 1px; height: 1px; clip-path: inset(50%); overflow: hidden; white-space: nowrap; }
.backup-controls label:has(+ input:focus-visible) { outline: 3px solid var(--orange); outline-offset: 4px; }
dialog { border: 1px solid #a2abc0; border-radius: 12px; padding: 32px; max-width: 540px; width: calc(100% - 32px); color: var(--ink); box-shadow: 0 25px 80px #15234740; }
dialog::backdrop { background: #15234790; }
dialog h2 { font-size: 1.8rem; }
#reset-error { color: var(--error); }
.alert { background: #fff2d5; color: #6c3900; padding: 18px 24px; max-width: 1200px; margin: 15px auto; font-size: .9rem; }
[hidden] { display: none !important; }
.about { max-width: 850px; }
.about h2 { margin-top: 40px; font-size: 1.7rem; }
.about .button { margin-top: 35px; }
.about li { margin-top: 10px; }
@media (prefers-reduced-motion: no-preference) {
  .welcome-lab { animation: arrive .6s cubic-bezier(.16,1,.3,1); }
  @keyframes arrive { from { clip-path: inset(0 0 8% 0 round 18px); } to { clip-path: inset(0 round 18px); } }
}
@media (max-width: 1020px) {
  .topbar { padding: 20px 28px; }
  .course-label { display: none; }
  main { padding: 32px 28px 55px; }
  .welcome { gap: 35px; }
  .welcome-lab { padding: 12px; border-radius: 15px 15px 40px 15px; }
  .experiment { padding: 18px; }
  .next-up { padding: 28px; }
  .lesson-workspace { gap: 30px; }
  .week-columns { gap: 18px; }
}
@media (max-width: 720px) {
  .course-switcher { padding: 16px 20px 0; gap: 10px; }
  .course-switcher select { width: 100%; }
  .course-switcher a { margin-left: 0; }
  .course-catalog li { flex-direction: column; align-items: flex-start; gap: 20px; }
  .qa-panel > summary { padding: 16px; }
  .qa-panel > summary span { display: block; margin: 5px 0 0 20px; }
  .qa-body { padding: 8px 16px 22px; }
  .qa-suggestions, .qa-choices, .qa-all-questions { flex-direction: column; align-items: stretch; }
  .qa-history { max-height: 480px; }
  .practice-entry { flex-direction: column; align-items: flex-start; gap: 20px; }
  .practice-round-list > li { flex-wrap: wrap; gap: 13px; }
  .practice-round-list > li > div { flex: 1; min-width: 220px; }
  .practice-round-list .button, .round-lock { margin-left: 53px; }
  .practice-levels li { padding: 12px 9px; }
  .practice-levels strong { font-size: .8rem; }
  .practice-levels span { font-size: .72rem; }
  .practice-question { padding: 22px 18px; }
  .practice-question-meta { flex-direction: column; gap: 6px; }
  .unit-checkpoint { flex-direction: column; align-items: flex-start; padding: 20px 16px; }
  .unit-progress > a, .topic-feedback li { flex-direction: column; gap: 5px; }
  .test-toolbar { align-items: flex-start; }
  .test-toolbar .button { padding: 10px 12px; font-size: .8rem; }
  .test-toolbar h2 { font-size: 1.2rem; }
  .topbar { padding: 16px 20px; flex-wrap: wrap; gap: 14px; }
  .brand { font-size: 1.13rem; }
  nav { width: 100%; gap: 3px; flex-wrap: wrap; }
  nav a { padding: 9px 12px; font-size: .83rem; }
  main { padding: 27px 20px 48px; }
  .welcome { grid-template-columns: 1fr; gap: 30px; padding-top: 3px; }
  .welcome-copy h1 { font-size: clamp(2.65rem, 10vw, 4.4rem); }
  .welcome-copy .lead { margin-top: 19px; font-size: 1.06rem; }
  .onboarding-note { display: none; }
  .welcome-lab { max-width: 480px; width: 100%; margin: auto; }
  .welcome .plot { max-height: 205px; }
  .program-section { margin-top: 15px; }
  .program-choices { grid-template-columns: 1fr; gap: 12px; }
  .program-choice { padding: 17px 19px; grid-template-columns: 1fr auto; }
  .program-choice:has(:checked) { padding: 16px 18px; }
  .program-choice .program-months { font-size: 1.9rem; margin-bottom: 7px; }
  .program-choice > span:not(.program-months) { margin-top: 4px; }
  .program-submit { flex-direction: column; align-items: flex-start; gap: 14px; }
  .dashboard-intro { align-items: flex-start; flex-direction: column; gap: 18px; }
  .dashboard-intro .lead { font-size: 1rem; }
  .study-workspace { grid-template-columns: 1fr; }
  .next-up { padding: 29px 25px; }
  .next-up h2 { font-size: 2rem; }
  .dashboard-graph { padding: 16px; }
  .dashboard-graph .plot { max-height: 280px; }
  .progress-strip { flex-direction: column; align-items: flex-start; gap: 20px; }
  progress { width: 100%; }
  .week-preview { grid-template-columns: 1fr; gap: 25px; }
  .unit-overview-item { gap: 15px; }
  .unit-block summary { padding: 19px 16px; font-size: 1.05rem; }
  .unit-completion { display: block; float: none; margin: 7px 0 0 19px; }
  .unit-description { padding: 3px 16px 16px; }
  .lesson-list a { padding: 17px 16px; flex-wrap: wrap; gap: 11px; }
  .lesson-list a > div { flex: 1; }
  .list-meta { width: 100%; text-align: left; padding-left: 41px; }
  .list-meta small { display: inline; margin-left: 12px; }
  .planner-key { flex-wrap: wrap; gap: 10px; }
  .planner-key .button { margin-left: 0; margin-top: 8px; }
  .planner-key > span { width: 100%; }
  .week summary { gap: 12px; flex-wrap: wrap; }
  .week summary strong { font-size: .85rem; flex: 1; }
  .week summary > span:first-of-type { min-width: 57px; font-size: .88rem; }
  .week-status { width: 100%; padding-left: 31px; }
  .week-content { padding: 0 10px 26px 31px; }
  .week-columns { grid-template-columns: 1fr; gap: 25px; }
  .lesson-breadcrumb { flex-direction: column; gap: 8px; }
  .lesson-heading h1 { font-size: 2.5rem; }
  .lesson-heading .lead { font-size: 1.08rem; }
  .lesson-workspace { grid-template-columns: 1fr; gap: 35px; }
  .lesson-experiment { position: static; }
  .lesson-reading > p { font-size: 1rem; }
  .quiz-section { margin-top: 45px; }
  .quiz-heading { align-items: flex-start; flex-direction: column; gap: 15px; }
  .answers { grid-template-columns: 1fr; }
  .question legend { font-size: 1rem; }
  .lesson-bottom { flex-direction: column; align-items: flex-start; gap: 12px; }
  footer { padding: 24px 20px; gap: 12px; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation: none !important; transition: none !important; }
}