/* ============================================================
   ENERGY PRIMER — Online course reader
   Calm, scholarly layout. Inter chrome + Newsreader body.
   ============================================================ */

.ep {
  --ep-bg:        #eef0f2;
  --ep-paper:     #ffffff;
  --ep-tint:      #e3e6e9;
  --ep-rule:      #cdd2d7;
  --ep-rule-soft: #dee2e6;
  --ep-ink:       #14171a;
  --ep-ink-2:     #282d33;
  --ep-ink-dim:   #565d66;
  --ep-ink-mute:  #838a93;
  --ep-accent:    #34616b;
  --ep-accent-2:  #284c54;
  --ep-mark:      #cfe0e3;

  --ep-mono: "JetBrains Mono", ui-monospace, monospace;
  --ep-sans: "Inter", -apple-system, BlinkMacSystemFont, sans-serif;
  --ep-serif: "Newsreader", ui-serif, Georgia, "Times New Roman", serif;

  font-family: var(--ep-sans);
  color: var(--ep-ink);
  background: var(--ep-bg);
  font-size: 14px;
}
.ep *, .ep *::before, .ep *::after { box-sizing: border-box; }
.ep button { font-family: inherit; cursor: pointer; border: 0; padding: 0; background: transparent; color: inherit; }
.ep a { color: inherit; }

/* ===================================================================
   COURSE SHELL — header bar, used on every primer view
   =================================================================== */
.ep-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 0 12px;
  border-bottom: 1px solid var(--ep-rule);
  margin-bottom: 28px;
  font-family: var(--ep-mono);
  font-size: 10.5px;
  letter-spacing: 0.14em;
  color: var(--ep-ink-mute);
}
.ep-bar-left { display: flex; align-items: center; gap: 14px; flex-wrap: wrap; }
.ep-bar-brand {
  display: inline-flex;
  align-items: center;
  gap: 9px;
  color: var(--ep-ink);
  text-transform: uppercase;
  font-weight: 700;
  letter-spacing: 0.18em;
}
.ep-bar-dot { width: 7px; height: 7px; background: var(--ep-accent); display: inline-block; }
.ep-bar-crumb {
  display: inline-flex;
  align-items: center;
  gap: 8px;
}
.ep-bar-crumb a { text-decoration: none; color: var(--ep-ink-dim); }
.ep-bar-crumb a:hover { color: var(--ep-accent); }
.ep-bar-sep { color: var(--ep-rule); }
.ep-bar-right { display: flex; align-items: center; gap: 16px; }
.ep-bar-prog {
  display: inline-flex;
  align-items: center;
  gap: 8px;
}
.ep-bar-prog-track {
  width: 96px;
  height: 4px;
  background: var(--ep-rule-soft);
  position: relative;
}
.ep-bar-prog-fill {
  position: absolute; inset: 0 auto 0 0;
  background: var(--ep-accent);
}

/* ===================================================================
   COURSE HOME
   =================================================================== */
.ep-home-hero {
  display: grid;
  grid-template-columns: minmax(0, 1.45fr) minmax(280px, 360px);
  gap: 56px;
  padding: 8px 0 44px;
  border-bottom: 1px solid var(--ep-rule);
  align-items: end;
}
.ep-home-eyebrow {
  font-family: var(--ep-mono);
  font-size: 10.5px;
  letter-spacing: 0.22em;
  color: var(--ep-accent);
  font-weight: 700;
  margin-bottom: 18px;
  text-transform: uppercase;
}
.ep-home-title {
  font-family: var(--ep-serif);
  font-size: clamp(40px, 5.4vw, 76px);
  font-weight: 500;
  line-height: 1.02;
  letter-spacing: -0.022em;
  color: var(--ep-ink);
  margin: 0 0 22px;
  text-wrap: balance;
  font-variation-settings: "opsz" 60;
}
.ep-home-title em { font-style: italic; color: var(--ep-accent-2); }
.ep-home-lede {
  font-family: var(--ep-serif);
  font-size: 19px;
  line-height: 1.5;
  color: var(--ep-ink-2);
  max-width: 56ch;
  margin: 0 0 30px;
  font-variation-settings: "opsz" 18;
}
.ep-home-cta {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  background: var(--ep-ink);
  color: var(--ep-paper);
  padding: 13px 22px;
  font-family: var(--ep-mono);
  font-size: 11.5px;
  font-weight: 700;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  white-space: nowrap;
}
.ep-home-cta:hover { background: var(--ep-accent); }
.ep-home-cta-secondary {
  margin-left: 12px;
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: var(--ep-ink-dim);
  font-family: var(--ep-mono);
  font-size: 11px;
  letter-spacing: 0.16em;
  font-weight: 600;
  text-transform: uppercase;
  text-decoration: none;
  padding: 13px 12px;
}
.ep-home-cta-secondary:hover { color: var(--ep-accent); }

.ep-home-meta {
  border-left: 1px solid var(--ep-rule);
  padding-left: 32px;
  display: flex;
  flex-direction: column;
  gap: 18px;
}
.ep-home-meta-row {
  display: flex;
  flex-direction: column;
  gap: 3px;
}
.ep-home-meta-lbl {
  font-family: var(--ep-mono);
  font-size: 9.5px;
  letter-spacing: 0.2em;
  color: var(--ep-ink-mute);
  text-transform: uppercase;
}
.ep-home-meta-val {
  font-family: var(--ep-serif);
  font-size: 22px;
  font-weight: 500;
  color: var(--ep-ink);
  line-height: 1.15;
}
.ep-home-meta-val small {
  font-size: 12px;
  color: var(--ep-ink-mute);
  font-family: var(--ep-mono);
  letter-spacing: 0.04em;
  display: block;
  margin-top: 2px;
}

/* "How to use" strip */
.ep-howto {
  margin: 48px 0;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 28px;
}
.ep-howto-item {
  padding-top: 14px;
  border-top: 2px solid var(--ep-ink);
}
.ep-howto-num {
  font-family: var(--ep-mono);
  font-size: 10px;
  letter-spacing: 0.2em;
  color: var(--ep-accent);
  font-weight: 700;
  margin-bottom: 6px;
}
.ep-howto-title {
  font-family: var(--ep-sans);
  font-size: 16px;
  font-weight: 700;
  color: var(--ep-ink);
  margin-bottom: 6px;
  letter-spacing: -0.005em;
}
.ep-howto-text {
  font-family: var(--ep-serif);
  font-size: 14.5px;
  line-height: 1.5;
  color: var(--ep-ink-dim);
}

/* Section heading on home */
.ep-home-secthead {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  padding-bottom: 14px;
  margin: 56px 0 22px;
  border-bottom: 1px solid var(--ep-rule);
}
.ep-home-secthead h2 {
  font-family: var(--ep-serif);
  font-size: 30px;
  font-weight: 500;
  letter-spacing: -0.014em;
  color: var(--ep-ink);
  margin: 0;
  font-variation-settings: "opsz" 32;
}
.ep-home-secthead-meta {
  font-family: var(--ep-mono);
  font-size: 10.5px;
  letter-spacing: 0.14em;
  color: var(--ep-ink-mute);
}

/* Sessions grid */
.ep-cards {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 14px;
}
.ep-card {
  display: block;
  padding: 22px 24px 20px;
  background: var(--ep-paper);
  border: 1px solid var(--ep-rule);
  text-decoration: none;
  color: inherit;
  transition: border-color 120ms, transform 120ms;
  position: relative;
}
.ep-card:hover { border-color: var(--ep-ink); }
.ep-card.is-done {
  background: var(--ep-tint);
}
.ep-card-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 12px;
}
.ep-card-num {
  font-family: var(--ep-mono);
  font-size: 10.5px;
  letter-spacing: 0.18em;
  color: var(--ep-accent);
  font-weight: 700;
}
.ep-card-pill {
  font-family: var(--ep-mono);
  font-size: 9px;
  letter-spacing: 0.18em;
  color: var(--ep-ink-mute);
  text-transform: uppercase;
  border: 1px solid var(--ep-rule);
  padding: 2px 7px;
}
.ep-card-pill.is-done {
  color: #2d7048;
  border-color: #2d7048;
  background: rgba(45, 112, 72, 0.06);
}
.ep-card-title {
  font-family: var(--ep-serif);
  font-size: 22px;
  font-weight: 500;
  line-height: 1.2;
  letter-spacing: -0.012em;
  color: var(--ep-ink);
  margin-bottom: 6px;
  font-variation-settings: "opsz" 24;
}
.ep-card-sub {
  font-family: var(--ep-serif);
  font-size: 14.5px;
  line-height: 1.5;
  color: var(--ep-ink-dim);
  font-style: italic;
  margin-bottom: 14px;
  font-variation-settings: "opsz" 14;
}
.ep-card-bs {
  font-family: var(--ep-mono);
  font-size: 10px;
  letter-spacing: 0.06em;
  color: var(--ep-ink-mute);
  border-top: 1px solid var(--ep-rule-soft);
  padding-top: 12px;
  margin-top: 8px;
  line-height: 1.5;
}
.ep-card-bs b {
  color: var(--ep-accent-2);
  font-weight: 700;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  display: block;
  margin-bottom: 4px;
  font-size: 9.5px;
}
.ep-card-foot {
  display: flex;
  justify-content: space-between;
  margin-top: 10px;
  font-family: var(--ep-mono);
  font-size: 10px;
  letter-spacing: 0.1em;
  color: var(--ep-ink-mute);
}
.ep-card-foot b {
  color: var(--ep-ink);
  font-weight: 700;
}

/* Resources block */
.ep-res {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
}
.ep-res-card {
  padding: 18px 18px 16px;
  background: var(--ep-paper);
  border: 1px solid var(--ep-rule);
  text-decoration: none;
  color: inherit;
  display: flex;
  flex-direction: column;
  gap: 6px;
  min-height: 130px;
}
.ep-res-card:hover { border-color: var(--ep-ink); }
.ep-res-tag {
  font-family: var(--ep-mono);
  font-size: 9.5px;
  letter-spacing: 0.2em;
  color: var(--ep-accent);
  font-weight: 700;
  text-transform: uppercase;
}
.ep-res-title {
  font-family: var(--ep-sans);
  font-size: 16px;
  font-weight: 700;
  color: var(--ep-ink);
  letter-spacing: -0.005em;
  margin-top: 6px;
}
.ep-res-sub {
  font-family: var(--ep-serif);
  font-size: 13.5px;
  line-height: 1.45;
  color: var(--ep-ink-dim);
  font-style: italic;
  margin-top: 2px;
}
.ep-res-foot {
  margin-top: auto;
  padding-top: 10px;
  font-family: var(--ep-mono);
  font-size: 10px;
  letter-spacing: 0.14em;
  color: var(--ep-ink-mute);
  display: flex;
  justify-content: space-between;
}

.ep-home-footnote {
  margin: 56px 0 0;
  padding-top: 18px;
  border-top: 1px solid var(--ep-rule);
  font-family: var(--ep-mono);
  font-size: 10.5px;
  letter-spacing: 0.08em;
  color: var(--ep-ink-mute);
  max-width: 80ch;
  line-height: 1.6;
}

/* ===================================================================
   READER VIEW — session pages
   =================================================================== */
.ep-reader {
  display: grid;
  grid-template-columns: 220px minmax(0, 1fr) 200px;
  gap: 44px;
  align-items: start;
  min-height: 60vh;
}

/* left rail: full course ToC */
.ep-side {
  position: sticky;
  top: 16px;
  align-self: start;
  max-height: calc(100vh - 32px);
  overflow-y: auto;
  font-family: var(--ep-mono);
}
.ep-side-title {
  font-size: 10px;
  letter-spacing: 0.22em;
  color: var(--ep-ink-mute);
  font-weight: 700;
  margin-bottom: 14px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--ep-rule);
}
.ep-side-list { list-style: none; margin: 0; padding: 0; display: flex; flex-direction: column; }
.ep-side-link {
  display: grid;
  grid-template-columns: 28px 1fr 14px;
  gap: 8px;
  padding: 8px 0;
  border-bottom: 1px solid var(--ep-rule-soft);
  font-size: 11px;
  color: var(--ep-ink-dim);
  text-decoration: none;
  letter-spacing: 0.02em;
  line-height: 1.35;
  align-items: start;
}
.ep-side-link:hover { color: var(--ep-ink); }
.ep-side-link.is-current { color: var(--ep-ink); }
.ep-side-link.is-current .ep-side-num { color: var(--ep-accent); }
.ep-side-num {
  font-weight: 700;
  color: var(--ep-ink-mute);
  letter-spacing: 0.16em;
}
.ep-side-name {
  font-family: var(--ep-sans);
  font-size: 12px;
  font-weight: 500;
  color: var(--ep-ink);
  letter-spacing: -0.005em;
  line-height: 1.35;
}
.ep-side-link.is-current .ep-side-name { color: var(--ep-accent); font-weight: 600; }
.ep-side-tick {
  color: #2d7048;
  font-size: 11px;
  font-weight: 700;
  text-align: right;
  line-height: 1.5;
}

.ep-side-sect {
  margin-top: 22px;
  font-size: 10px;
  letter-spacing: 0.22em;
  color: var(--ep-ink-mute);
  font-weight: 700;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--ep-rule);
}

/* main reader */
.ep-main { min-width: 0; }

.ep-eyebrow {
  font-family: var(--ep-mono);
  font-size: 10.5px;
  letter-spacing: 0.22em;
  color: var(--ep-accent);
  font-weight: 700;
  margin-bottom: 14px;
  text-transform: uppercase;
}
.ep-main h1.ep-h1 {
  font-family: var(--ep-serif);
  font-size: clamp(36px, 4vw, 56px);
  font-weight: 500;
  line-height: 1.04;
  letter-spacing: -0.02em;
  color: var(--ep-ink);
  margin: 0 0 16px;
  font-variation-settings: "opsz" 60;
  text-wrap: balance;
}
.ep-main-sub {
  font-family: var(--ep-serif);
  font-size: 19px;
  line-height: 1.5;
  color: var(--ep-ink-dim);
  font-style: italic;
  margin: 0 0 26px;
  max-width: 62ch;
  font-variation-settings: "opsz" 18;
}
.ep-spec {
  display: grid;
  grid-template-columns: repeat(3, auto);
  gap: 28px 36px;
  padding: 18px 0 22px;
  border-top: 1px solid var(--ep-rule);
  border-bottom: 1px solid var(--ep-rule);
  margin-bottom: 38px;
}
.ep-spec-row { display: flex; flex-direction: column; gap: 4px; }
.ep-spec-row b {
  font-family: var(--ep-mono);
  font-size: 9.5px;
  letter-spacing: 0.18em;
  color: var(--ep-ink-mute);
  font-weight: 700;
  text-transform: uppercase;
}
.ep-spec-row span {
  font-family: var(--ep-sans);
  font-size: 14.5px;
  font-weight: 500;
  color: var(--ep-ink);
  letter-spacing: -0.005em;
}

/* prose */
.ep-prose {
  font-family: var(--ep-serif);
  font-size: 17.5px;
  line-height: 1.6;
  color: var(--ep-ink-2);
  max-width: 68ch;
  font-variation-settings: "opsz" 17;
}
.ep-prose > * + * { margin-top: 1em; }
.ep-prose p { margin: 0; }
.ep-prose h2 {
  font-family: var(--ep-sans);
  font-size: 22px;
  font-weight: 700;
  color: var(--ep-ink);
  margin: 56px 0 16px;
  letter-spacing: -0.012em;
  line-height: 1.2;
  padding-top: 18px;
  border-top: 1px solid var(--ep-rule);
  scroll-margin-top: 24px;
  text-wrap: balance;
}
.ep-prose h2 .h2-mark {
  font-family: var(--ep-mono);
  font-size: 10.5px;
  font-weight: 700;
  color: var(--ep-accent);
  display: block;
  letter-spacing: 0.22em;
  margin-bottom: 6px;
}
.ep-prose h3 {
  font-family: var(--ep-sans);
  font-size: 16px;
  font-weight: 700;
  color: var(--ep-ink);
  margin: 32px 0 8px;
  letter-spacing: -0.005em;
  line-height: 1.3;
  scroll-margin-top: 24px;
}
.ep-prose h4 {
  font-family: var(--ep-sans);
  font-size: 14px;
  font-weight: 700;
  color: var(--ep-ink);
  margin: 18px 0 4px;
  letter-spacing: 0;
}
.ep-prose strong { color: var(--ep-ink); font-weight: 600; }
.ep-prose em { font-style: italic; }
.ep-prose ul, .ep-prose ol {
  padding-left: 1.4em;
  margin: 1em 0;
}
.ep-prose li { margin: 0.45em 0; }
.ep-prose li::marker { color: var(--ep-ink-mute); }
.ep-prose ul li::marker { content: "— "; font-family: var(--ep-mono); }
.ep-prose a {
  color: var(--ep-accent);
  text-decoration: underline;
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
  text-decoration-color: rgba(163, 96, 26, 0.4);
}
.ep-prose a:hover { text-decoration-color: var(--ep-accent); }
.ep-prose hr {
  border: 0;
  border-top: 1px solid var(--ep-rule);
  margin: 36px 0;
}
.ep-prose blockquote {
  margin: 24px 0;
  padding: 14px 20px;
  border-left: 3px solid var(--ep-accent);
  background: var(--ep-tint);
  font-style: italic;
  color: var(--ep-ink-2);
}
.ep-prose code {
  font-family: var(--ep-mono);
  font-size: 0.86em;
  background: var(--ep-tint);
  padding: 1px 5px;
  letter-spacing: 0;
}
.ep-prose pre {
  font-family: var(--ep-mono);
  font-size: 13px;
  background: var(--ep-tint);
  border: 1px solid var(--ep-rule);
  padding: 12px 14px;
  overflow-x: auto;
  line-height: 1.45;
}
.ep-prose pre code {
  background: transparent;
  padding: 0;
}

/* tables — make them feel reference-y */
.ep-prose table {
  width: 100%;
  border-collapse: collapse;
  margin: 22px 0;
  font-family: var(--ep-sans);
  font-size: 13.5px;
  background: var(--ep-paper);
  border: 1px solid var(--ep-rule);
}
.ep-prose thead { background: var(--ep-tint); }
.ep-prose th {
  font-family: var(--ep-mono);
  font-size: 10px;
  letter-spacing: 0.16em;
  color: var(--ep-ink-mute);
  font-weight: 700;
  text-transform: uppercase;
  text-align: left;
  padding: 9px 14px;
  border-bottom: 1px solid var(--ep-rule);
  vertical-align: top;
}
.ep-prose td {
  padding: 9px 14px;
  border-bottom: 1px solid var(--ep-rule-soft);
  vertical-align: top;
  color: var(--ep-ink-2);
}
.ep-prose tr:last-child td { border-bottom: 0; }

/* first paragraph of body — subtle introduction, no drop cap */
.ep-prose > p:first-child {
  font-size: 19px;
  color: var(--ep-ink);
  line-height: 1.55;
  font-variation-settings: "opsz" 19;
}

/* right rail: on-this-page */
.ep-onpage {
  position: sticky;
  top: 16px;
  align-self: start;
  max-height: calc(100vh - 32px);
  overflow-y: auto;
  font-family: var(--ep-mono);
}
.ep-onpage-title {
  font-size: 10px;
  letter-spacing: 0.22em;
  color: var(--ep-ink-mute);
  font-weight: 700;
  margin-bottom: 12px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--ep-rule);
}
.ep-onpage-list { list-style: none; margin: 0; padding: 0; display: flex; flex-direction: column; gap: 6px; }
.ep-onpage-list a {
  display: block;
  font-family: var(--ep-sans);
  font-size: 12px;
  color: var(--ep-ink-dim);
  text-decoration: none;
  line-height: 1.35;
  padding: 3px 0 3px 10px;
  border-left: 2px solid transparent;
  letter-spacing: -0.005em;
}
.ep-onpage-list a:hover { color: var(--ep-accent); }
.ep-onpage-list a.is-active {
  color: var(--ep-ink);
  border-left-color: var(--ep-accent);
  font-weight: 600;
}

.ep-onpage-meta {
  margin-top: 22px;
  padding-top: 14px;
  border-top: 1px solid var(--ep-rule);
  display: flex;
  flex-direction: column;
  gap: 10px;
  font-family: var(--ep-mono);
  font-size: 10px;
  letter-spacing: 0.14em;
  color: var(--ep-ink-mute);
}
.ep-onpage-meta b { color: var(--ep-ink); letter-spacing: 0.16em; font-weight: 700; }
.ep-onpage-actions { display: flex; gap: 8px; margin-top: 6px; }
.ep-onpage-btn {
  flex: 1;
  text-align: center;
  border: 1px solid var(--ep-rule);
  padding: 6px 8px;
  font-family: var(--ep-mono);
  font-size: 10px;
  letter-spacing: 0.12em;
  color: var(--ep-ink-dim);
  text-transform: uppercase;
}
.ep-onpage-btn:hover { border-color: var(--ep-accent); color: var(--ep-accent); }
.ep-onpage-btn.is-done { background: #2d7048; color: #fff; border-color: #2d7048; }

/* footer of session: prev / next */
.ep-pager {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
  margin: 60px 0 0;
  padding-top: 24px;
  border-top: 1px solid var(--ep-rule);
}
.ep-pager-card {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 18px 20px;
  border: 1px solid var(--ep-rule);
  background: var(--ep-paper);
  text-decoration: none;
  color: inherit;
}
.ep-pager-card:hover { border-color: var(--ep-ink); }
.ep-pager-card.is-next { text-align: right; }
.ep-pager-lbl {
  font-family: var(--ep-mono);
  font-size: 9.5px;
  letter-spacing: 0.22em;
  color: var(--ep-ink-mute);
  font-weight: 700;
  text-transform: uppercase;
}
.ep-pager-title {
  font-family: var(--ep-serif);
  font-size: 17px;
  font-weight: 500;
  color: var(--ep-ink);
  letter-spacing: -0.01em;
  line-height: 1.3;
}
.ep-pager-empty {
  border: 1px dashed var(--ep-rule);
  background: transparent;
}
.ep-pager-empty .ep-pager-title { color: var(--ep-ink-mute); font-style: italic; }

/* loading state */
.ep-loading {
  font-family: var(--ep-mono);
  font-size: 11px;
  letter-spacing: 0.16em;
  color: var(--ep-ink-mute);
  padding: 60px 0;
  text-align: center;
}
.ep-loading-bar {
  width: 120px;
  height: 2px;
  background: var(--ep-rule);
  margin: 14px auto 0;
  position: relative;
  overflow: hidden;
}
.ep-loading-bar::after {
  content: "";
  position: absolute;
  top: 0; left: 0; bottom: 0;
  width: 40%;
  background: var(--ep-accent);
  animation: ep-load 1.1s ease-in-out infinite;
}
@keyframes ep-load {
  0%   { left: -40%; }
  100% { left: 100%; }
}

/* responsive: collapse rails */
@media (max-width: 1280px) {
  .ep-reader { grid-template-columns: 200px minmax(0, 1fr); }
  .ep-onpage { display: none; }
}
@media (max-width: 980px) {
  .ep-reader { grid-template-columns: minmax(0, 1fr); }
  .ep-side { display: none; }
  .ep-howto, .ep-res, .ep-cards { grid-template-columns: 1fr 1fr; }
  .ep-home-hero { grid-template-columns: 1fr; gap: 24px; }
  .ep-home-meta { border-left: 0; padding-left: 0; border-top: 1px solid var(--ep-rule); padding-top: 18px; }
}
@media (max-width: 640px) {
  .ep-howto, .ep-res, .ep-cards { grid-template-columns: 1fr; }
  .ep-spec { grid-template-columns: 1fr 1fr; }
}