.lesson-page {
  --chapter-accent: var(--pink);
  --chapter-soft: #fff0f6;
  --chapter-dark: #250715;
  background: #f5f5f2;
  overflow-x: clip;
}

.lesson-page--2 {
  --chapter-accent: #ff7a00;
  --chapter-soft: #fff4e7;
  --chapter-dark: #281402;
}

.lesson-page--3 {
  --chapter-accent: #15d66f;
  --chapter-soft: #ecfff4;
  --chapter-dark: #032514;
}

.lesson-page--4 {
  --chapter-accent: #49aef2;
  --chapter-soft: #edf8ff;
  --chapter-dark: #031d2e;
}

.lesson-page--5 {
  --chapter-accent: #a36af2;
  --chapter-soft: #f7efff;
  --chapter-dark: #1c082f;
}

.lesson-page--6 {
  --chapter-accent: #ff7659;
  --chapter-soft: #fff1ed;
  --chapter-dark: #321007;
}

.lesson-page--7 {
  --chapter-accent: #f4cf27;
  --chapter-soft: #fffbea;
  --chapter-dark: #2b2402;
}

.lesson-page--8 {
  --chapter-accent: #2bcac2;
  --chapter-soft: #eafffd;
  --chapter-dark: #032927;
}

.lesson-page--9 {
  --chapter-accent: #8dde45;
  --chapter-soft: #f3ffe9;
  --chapter-dark: #153002;
}

.reading-progress {
  position: fixed;
  z-index: 120;
  top: 0;
  left: 0;
  width: 100%;
  height: 4px;
  background: linear-gradient(90deg, var(--chapter-accent) var(--reading-progress, 0%), transparent 0);
  pointer-events: none;
}

.lesson-header {
  position: sticky;
  z-index: 100;
  top: 0;
  height: 76px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 clamp(18px, 4vw, 52px);
  border-bottom: 1px solid rgba(0, 0, 0, 0.12);
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(16px);
}

.lesson-brand {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  font-weight: 700;
  letter-spacing: -0.025em;
}

.lesson-brand__mark {
  width: 42px;
  height: 42px;
  border-width: 3px;
}

.lesson-brand__mark img {
  inset: 6px;
  width: 24px;
  height: 24px;
  object-fit: contain;
}

.lesson-header__actions {
  display: flex;
  align-items: center;
  gap: 20px;
  font-size: 14px;
  font-weight: 600;
}

.lesson-header__actions > a {
  position: relative;
}

.lesson-header__actions > a::after {
  position: absolute;
  right: 0;
  bottom: -5px;
  left: 0;
  height: 2px;
  background: var(--chapter-accent);
  content: "";
  transform: scaleX(0);
  transition: transform 160ms ease;
}

.lesson-header__actions > a:hover::after {
  transform: scaleX(1);
}

.lesson-menu-button {
  width: 44px;
  height: 44px;
  display: none;
  place-content: center;
  gap: 5px;
  border-radius: 50%;
  background: var(--ink);
  color: var(--paper);
  cursor: pointer;
}

.lesson-menu-button span:not(.visually-hidden) {
  width: 19px;
  height: 2px;
  border-radius: 2px;
  background: currentColor;
}

.lesson-shell {
  width: min(100%, 1540px);
  display: grid;
  grid-template-columns: 300px minmax(0, 1fr);
  margin: 0 auto;
}

.lesson-sidebar {
  position: relative;
  border-right: 1px solid rgba(0, 0, 0, 0.12);
}

.lesson-sidebar__inner {
  position: sticky;
  top: 76px;
  max-height: calc(100vh - 76px);
  overflow-y: auto;
  padding: 42px 28px 52px;
  scrollbar-width: thin;
}

.lesson-sidebar__eyebrow {
  margin: 0 0 12px;
  color: var(--muted);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.lesson-sidebar__eyebrow--sections {
  margin-top: 42px;
}

.lesson-chapters,
.lesson-sections {
  display: grid;
  gap: 6px;
}

.lesson-chapters a {
  display: grid;
  grid-template-columns: 32px 1fr;
  gap: 8px;
  align-items: center;
  padding: 10px;
  border-radius: 12px;
  color: #565656;
  font-size: 13px;
  line-height: 1.35;
}

.lesson-chapters a span {
  font-size: 10px;
  font-weight: 700;
}

.lesson-chapters a:hover,
.lesson-chapters a[aria-current="page"] {
  background: var(--ink);
  color: var(--paper);
}

.lesson-chapters a[aria-current="page"] span {
  color: var(--chapter-accent);
}

.lesson-sections a {
  position: relative;
  padding: 8px 8px 8px 16px;
  border-radius: 9px;
  color: #626262;
  font-size: 12px;
  line-height: 1.45;
}

.lesson-sections a::before {
  position: absolute;
  top: 14px;
  left: 2px;
  width: 5px;
  height: 5px;
  border-radius: 50%;
  background: #c8c8c8;
  content: "";
}

.lesson-sections a:hover,
.lesson-sections a.is-current {
  background: var(--chapter-soft);
  color: var(--ink);
}

.lesson-sections a.is-current::before {
  background: var(--chapter-accent);
}

.lesson-main {
  min-width: 0;
  padding: 32px clamp(20px, 5vw, 72px) 50px;
}

.breadcrumbs {
  width: min(100%, 980px);
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 0 auto 24px;
  color: var(--muted);
  font-size: 12px;
}

.breadcrumbs a:hover {
  color: var(--ink);
  text-decoration: underline;
}

.lesson-hero {
  position: relative;
  width: min(100%, 980px);
  min-height: 340px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  margin: 0 auto 24px;
  padding: clamp(28px, 6vw, 64px);
  overflow: hidden;
  border: 3px solid var(--ink);
  border-radius: 42px;
  background: var(--chapter-accent);
  color: var(--chapter-dark);
  isolation: isolate;
}

.lesson-hero::before,
.lesson-hero::after,
.lesson-hero__shape {
  position: absolute;
  z-index: -1;
  border: 3px solid var(--ink);
  content: "";
}

.lesson-hero::before {
  top: -120px;
  right: -60px;
  width: 330px;
  height: 330px;
  border-radius: 50%;
  background: var(--yellow);
}

.lesson-hero::after {
  top: 70px;
  right: 145px;
  width: 115px;
  height: 115px;
  border-radius: 26px;
  background: var(--paper);
  transform: rotate(18deg);
}

.lesson-hero__shape {
  right: 54px;
  bottom: -60px;
  width: 190px;
  height: 190px;
  border-radius: 50% 50% 12% 50%;
  background: var(--blue);
  transform: rotate(-20deg);
}

.lesson-hero p {
  margin: 0 0 18px;
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.lesson-hero h1 {
  min-width: 0;
  max-width: 720px;
  margin: 0;
  font-size: clamp(42px, 6vw, 78px);
  font-weight: 600;
  line-height: 0.98;
  letter-spacing: -0.055em;
  overflow-wrap: anywhere;
}

.lesson-content {
  width: min(100%, 980px);
  margin: 0 auto;
  padding: clamp(28px, 5vw, 68px);
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 36px;
  background: var(--paper);
  box-shadow: 0 20px 70px rgba(0, 0, 0, 0.055);
  font-family: "Inter", Arial, sans-serif;
  font-size: 16px;
  line-height: 1.75;
}

.lesson-content .part-wrapper,
.lesson-content .part,
.lesson-content .chapter,
.lesson-content .ugc {
  min-width: 0;
  max-width: 100%;
}

.lesson-content .part-wrapper {
  overflow: hidden;
}

.lesson-content .part {
  margin-bottom: 72px;
  padding: clamp(24px, 4vw, 42px);
  border: 2px solid var(--ink);
  border-radius: 28px;
  background: var(--chapter-soft);
}

.lesson-content .part-number {
  width: 44px;
  height: 44px;
  display: grid;
  place-items: center;
  margin: 0 0 30px;
  border-radius: 50%;
  background: var(--ink);
  color: var(--paper);
  font-size: 13px;
  font-weight: 700;
}

.lesson-content .part-title,
.lesson-content .chapter-title {
  color: var(--ink);
  font-family: "Inter", Arial, sans-serif;
}

.lesson-content .part-title {
  margin: 0 0 28px;
  font-size: clamp(30px, 4vw, 48px);
  line-height: 1.08;
  letter-spacing: -0.04em;
  overflow-wrap: anywhere;
}

.lesson-content .part-ugc > :first-child,
.lesson-content .chapter-ugc > :first-child {
  margin-top: 0;
}

.lesson-content .chapter {
  padding-top: 72px;
  scroll-margin-top: 94px;
}

.lesson-content .chapter + .chapter {
  margin-top: 86px;
  border-top: 2px solid var(--ink);
}

.lesson-content .chapter-title-wrap {
  position: relative;
  margin-bottom: 42px;
  padding-right: 70px;
}

.lesson-content .chapter-number {
  position: absolute;
  top: 0;
  right: 0;
  width: 48px;
  height: 48px;
  display: grid;
  place-items: center;
  margin: 0;
  border: 2px solid var(--ink);
  border-radius: 50%;
  background: var(--yellow);
  font-size: 13px;
  font-weight: 700;
}

.lesson-content .chapter-title {
  margin: 0;
  font-size: clamp(34px, 5vw, 58px);
  line-height: 1.04;
  letter-spacing: -0.05em;
  overflow-wrap: anywhere;
}

.lesson-content h3 {
  margin: 60px 0 20px;
  font-size: clamp(24px, 3vw, 34px);
  line-height: 1.2;
  letter-spacing: -0.025em;
}

.lesson-content h4 {
  margin: 42px 0 16px;
  font-size: 20px;
  line-height: 1.3;
}

.lesson-content p {
  margin: 0 0 1.15em;
}

.lesson-content a:not(.lesson-pager__link) {
  color: #1738c8;
  text-decoration: underline;
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
}

.lesson-content a[target="_blank"]::after {
  width: 0.78em;
  height: 0.78em;
  display: inline-block;
  margin-left: 0.25em;
  background: url("../icons/external-link.svg") center / contain no-repeat;
  content: "";
}

.lesson-content strong {
  font-weight: 700;
}

.lesson-content ul,
.lesson-content ol {
  margin: 1em 0 1.5em;
  padding-left: 1.55em;
}

.lesson-content li + li {
  margin-top: 0.5em;
}

.lesson-content hr {
  margin: 48px 0;
  border: 0;
  border-top: 1px solid var(--line);
}

.lesson-content [data-type="media"] > img,
.lesson-content p > img:not(.ql-img-inline-formula),
.lesson-content .wp-caption img,
.lesson-content .bc-figure img,
.lesson-content .splash img {
  width: auto;
  max-width: 100%;
  height: auto;
  margin: 26px auto;
  border-radius: 16px;
}

.lesson-content .ql-img-inline-formula {
  width: auto;
  max-width: min(100%, 620px);
  height: auto;
  display: inline-block;
  margin: 0 0.16em;
  border-radius: 0;
  vertical-align: middle !important;
}

.lesson-content .aligncenter {
  margin-right: auto !important;
  margin-left: auto !important;
}

.lesson-content .alignleft,
.lesson-content .alignright {
  max-width: 48%;
  margin-bottom: 20px;
}

.lesson-content .alignleft {
  float: left;
  margin-right: 24px;
}

.lesson-content .alignright {
  float: right;
  margin-left: 24px;
}

.lesson-content .wp-caption {
  width: auto !important;
  max-width: 100%;
  margin: 28px auto;
  padding: 12px;
  border-radius: 18px;
  background: #f4f4f4;
}

.lesson-content .wp-caption img {
  margin: 0 auto;
}

.lesson-content .wp-caption-text,
.lesson-content .bc-figcaption,
.lesson-content .figcaption {
  margin: 12px 0 0;
  color: var(--muted);
  font-size: 12px;
  line-height: 1.55;
}

.lesson-content .lesson-attribution-figure {
  width: fit-content;
  max-width: 100%;
  margin: 28px auto;
}

.lesson-content .wp-caption .lesson-attribution-figure {
  margin: 0 auto;
}

.lesson-content .lesson-attribution-figure > img {
  max-width: 100%;
  height: auto;
  display: block;
  margin: 0 auto;
  border-radius: 16px;
}

.lesson-content .lesson-attribution-caption {
  max-width: 74ch;
  margin: 10px auto 0;
  color: #4b4b4b;
  font-size: 13px;
  line-height: 1.55;
  text-align: left;
}

.lesson-content .lesson-attribution-caption a {
  color: inherit;
  font-weight: 600;
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
}

.lesson-content .table-scroll {
  width: 100%;
  margin: 26px 0;
  overflow-x: auto;
  border: 1px solid var(--line);
  border-radius: 16px;
  -webkit-overflow-scrolling: touch;
}

.lesson-content table {
  width: 100% !important;
  min-width: 540px;
  margin: 0;
  border-collapse: collapse !important;
  background: var(--paper);
  font-size: 14px;
  line-height: 1.5;
}

.lesson-content th,
.lesson-content td {
  min-width: 96px;
  padding: 12px 14px;
  border: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
}

.lesson-content th {
  background: var(--ink);
  color: var(--paper);
  font-weight: 700;
}

.lesson-content tr:nth-child(even) td {
  background: #fafafa;
}

.lesson-content .textbox {
  margin: 30px 0;
  overflow: hidden;
  border: 2px solid var(--ink);
  border-radius: 20px;
  background: var(--paper);
}

.lesson-content .textbox__header {
  padding: 13px 18px;
  background: var(--ink);
  color: var(--paper);
}

.lesson-content .textbox__title {
  margin: 0;
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.06em;
  line-height: 1.45;
  text-transform: uppercase;
}

.lesson-content .textbox__content {
  padding: 22px;
}

.lesson-content .textbox__content > :last-child {
  margin-bottom: 0;
}

.lesson-content .textbox--learning-objectives {
  border-color: var(--chapter-accent);
  background: var(--chapter-soft);
}

.lesson-content .textbox--learning-objectives .textbox__header {
  background: var(--chapter-accent);
  color: var(--chapter-dark);
}

.lesson-content .textbox--examples {
  border-color: #4b44e8;
}

.lesson-content .textbox--examples .textbox__header {
  background: #4b44e8;
}

.lesson-content .textbox--exercises {
  border-color: #0f9b54;
}

.lesson-content .textbox--exercises .textbox__header {
  background: #0f9b54;
}

.lesson-content .textbox--key-takeaways {
  border-color: var(--ink);
  background: var(--yellow);
}

.lesson-content .textbox--key-takeaways .textbox__header {
  color: var(--yellow);
}

.lesson-content [data-type="solution"] > [data-type="title"] strong {
  display: inline-block;
  margin: 8px 0 12px;
  padding: 5px 10px;
  border-radius: 999px;
  background: #ececec;
  font-size: 12px;
}

.lesson-content details.bc-details {
  margin-top: 16px;
  border: 1px solid #b9d9c8;
  border-radius: 13px;
  background: #f2fff8;
}

.lesson-content details.bc-details summary {
  padding: 11px 14px;
  cursor: pointer;
  font-size: 13px;
  font-weight: 700;
}

.lesson-content details.bc-details > :not(summary) {
  margin-right: 14px;
  margin-left: 14px;
}

.lesson-content .autogenerated-content {
  margin-top: 20px;
  padding: 18px;
  border-radius: 16px;
  background: #f5f5f5;
}

.lesson-content::after {
  display: block;
  clear: both;
  content: "";
}

.lesson-pager {
  width: min(100%, 980px);
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin: 24px auto 0;
}

.lesson-pager__link {
  min-height: 130px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  padding: 24px;
  border: 2px solid var(--ink);
  border-radius: 24px;
  background: var(--paper);
  transition: background 160ms ease, color 160ms ease, transform 160ms ease;
}

.lesson-pager__link--next {
  align-items: flex-end;
  text-align: right;
}

.lesson-pager__link span {
  margin-bottom: 7px;
  color: var(--muted);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.lesson-pager__link strong {
  font-size: 18px;
}

.lesson-pager__link:hover {
  background: var(--ink);
  color: var(--paper);
  transform: translateY(-4px);
}

.lesson-pager__link:hover span {
  color: var(--chapter-accent);
}

.lesson-footer {
  margin-top: 54px;
}

@media (max-width: 1060px) {
  .lesson-shell {
    display: block;
  }

  .lesson-sidebar {
    position: fixed;
    z-index: 90;
    top: 76px;
    right: 0;
    bottom: 0;
    width: min(340px, 88vw);
    border: 0;
    background: var(--paper);
    box-shadow: -20px 0 60px rgba(0, 0, 0, 0.18);
    transform: translateX(110%);
    transition: transform 220ms ease;
  }

  .lesson-nav-open .lesson-sidebar {
    transform: translateX(0);
  }

  .lesson-sidebar__inner {
    position: static;
    max-height: 100%;
  }

  .lesson-menu-button {
    display: grid;
  }

  .lesson-main {
    padding-right: clamp(16px, 4vw, 42px);
    padding-left: clamp(16px, 4vw, 42px);
  }
}

@media (max-width: 680px) {
  .lesson-header {
    height: 68px;
    padding-right: 14px;
    padding-left: 14px;
  }

  .lesson-brand > span:last-child,
  .lesson-header__actions > a {
    display: none;
  }

  .lesson-sidebar {
    top: 68px;
  }

  .lesson-main {
    padding: 18px 0 32px;
  }

  .breadcrumbs {
    width: calc(100% - 28px);
  }

  .lesson-hero {
    width: calc(100% - 20px);
    min-height: 300px;
    padding: 28px;
    border-radius: 30px;
  }

  .lesson-hero::before {
    right: -140px;
  }

  .lesson-hero::after,
  .lesson-hero__shape {
    opacity: 0.72;
    transform: scale(0.72) rotate(18deg);
  }

  .lesson-hero h1 {
    font-size: clamp(38px, 12vw, 58px);
  }

  .lesson-content {
    padding: 34px 18px;
    border-right: 0;
    border-left: 0;
    border-radius: 0;
    font-size: 15px;
  }

  .lesson-content .part {
    margin-bottom: 52px;
    padding: 24px 18px;
    border-radius: 22px;
  }

  .lesson-content .chapter {
    padding-top: 50px;
  }

  .lesson-content .chapter + .chapter {
    margin-top: 62px;
  }

  .lesson-content .chapter-title-wrap {
    padding-right: 52px;
  }

  .lesson-content .chapter-number {
    width: 40px;
    height: 40px;
  }

  .lesson-content .alignleft,
  .lesson-content .alignright {
    max-width: 100%;
    float: none;
    margin-right: auto;
    margin-left: auto;
  }

  .lesson-content .textbox__content {
    padding: 17px;
  }

  .lesson-pager {
    width: calc(100% - 20px);
    grid-template-columns: 1fr;
  }

}

@media print {
  .lesson-header,
  .lesson-sidebar,
  .breadcrumbs,
  .lesson-pager,
  .lesson-footer,
  .reading-progress {
    display: none !important;
  }

  .lesson-page,
  .lesson-main,
  .lesson-content {
    background: white;
  }

  .lesson-main,
  .lesson-content {
    width: 100%;
    max-width: none;
    padding: 0;
    border: 0;
    box-shadow: none;
  }

  .lesson-hero {
    min-height: 0;
    padding: 32px;
    break-after: page;
  }

  .lesson-content .chapter {
    break-before: page;
  }
}