/* ---------------------------------------------------------------------------
   Design tokens
   Change these to reskin the site; the rules below reference them only.
   --------------------------------------------------------------------------- */
:root {
  /* Greys match perimeterinstitute.ca (--color-black / --color-grey-dk). */
  --color-text: #2d2d2d;
  --color-muted: #474747;
  --color-bg: #ffffff;
  --color-surface: #f7f8fa;
  /* Matches perimeterinstitute.ca, whose theme sets links to --color-blue. */
  --color-accent: #0b75b7;
  --color-accent-hover: #095c8f;
  --color-border: #e2e5ea;

  --font-body: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    "Helvetica Neue", Arial, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas,
    "Liberation Mono", monospace;

  /* Content column. --size-container-wide is the header/footer track, which
     runs wider so the nav spreads out instead of crowding the site title. */
  --size-container: 54rem;
  --size-container-wide: 84rem;
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 2rem;
  --space-xl: 3rem;

  --radius: 4px;
}

/* ---------------------------------------------------------------------------
   Base
   --------------------------------------------------------------------------- */
*,
*::before,
*::after {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: var(--font-body);
  font-size: 1.0625rem;
  line-height: 1.65;
  color: var(--color-text);
  background: var(--color-bg);
  -webkit-font-smoothing: antialiased;
}

.container,
.container-wide {
  width: 100%;
  margin-inline: auto;
  padding-inline: var(--space-md);
}

.container {
  max-width: var(--size-container);
}

.container-wide {
  max-width: var(--size-container-wide);
}

h1,
h2,
h3 {
  line-height: 1.25;
  margin-block: var(--space-lg) var(--space-md);
  text-wrap: balance;
}

h1 {
  font-size: 2rem;
}
h2 {
  font-size: 1.375rem;
}
h3 {
  font-size: 1.125rem;
}

p,
ul,
ol {
  margin-block: 0 var(--space-md);
}

a {
  color: var(--color-accent);
  text-decoration-thickness: 1px;
  text-underline-offset: 2px;
}

a:hover {
  color: var(--color-accent-hover);
}

img {
  max-width: 100%;
  height: auto;
}

code {
  font-family: var(--font-mono);
  font-size: 0.9em;
  background: var(--color-surface);
  padding: 0.15em 0.35em;
  border-radius: var(--radius);
}

pre {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: var(--space-md);
  overflow-x: auto;
}

pre code {
  background: none;
  padding: 0;
}

/* Keyboard-only skip link. */
.skip-link {
  position: absolute;
  left: -9999px;
}

.skip-link:focus {
  left: var(--space-md);
  top: var(--space-md);
  z-index: 10;
  background: var(--color-bg);
  padding: var(--space-sm) var(--space-md);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
}

/* ---------------------------------------------------------------------------
   Header / nav
   --------------------------------------------------------------------------- */
.site-header {
  border-bottom: 1px solid var(--color-border);
  background: var(--color-bg);
  /* Keeps the small-screen dropdown painting above the page content. */
  position: relative;
  z-index: 10;
}

.header-inner {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-md);
  padding-block: var(--space-md);
}

.site-title {
  font-weight: 700;
  font-size: 1.375rem;
  color: var(--color-text);
  text-decoration: none;
}

/* Anchors the small-screen dropdown. */
.site-nav {
  position: relative;
}

/* The toggle is a visually hidden checkbox driving its label, so the open
   state is pure CSS. Kept in the layout (not display:none) so it stays
   focusable and operable by keyboard. */
.nav-checkbox {
  position: absolute;
  width: 1px;
  height: 1px;
  opacity: 0;
  pointer-events: none;
}

.nav-toggle {
  display: inline-block;
  cursor: pointer;
  font-size: 1.125rem;
  color: var(--color-muted);
}

.nav-toggle:hover {
  color: var(--color-accent);
}

.nav-checkbox:focus-visible + .nav-toggle {
  outline: 2px solid var(--color-accent);
  outline-offset: 3px;
  border-radius: var(--radius);
}

/* Small screens: hidden until the toggle is checked, then floated over the
   page rather than pushing it down. */
.nav {
  display: none;
  position: absolute;
  top: calc(100% + var(--space-sm));
  right: 0;
  z-index: 20;
  min-width: 12rem;
  flex-direction: column;
  gap: var(--space-sm);
  font-size: 1.125rem;
  list-style: none;
  margin: 0;
  padding: var(--space-md);
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  box-shadow: 0 6px 20px rgb(0 0 0 / 12%);
}

.nav-checkbox:checked ~ .nav {
  display: flex;
}

/* From 40em up the toggle disappears and the list is a plain row again. */
@media (min-width: 40em) {
  .nav-checkbox,
  .nav-toggle {
    display: none;
  }

  .nav {
    display: flex;
    position: static;
    z-index: auto;
    min-width: 0;
    flex-direction: row;
    flex-wrap: wrap;
    gap: var(--space-lg);
    padding: 0;
    background: none;
    border: 0;
    border-radius: 0;
    box-shadow: none;
  }
}

.nav a {
  color: var(--color-muted);
  text-decoration: none;
}

.nav a:hover,
.nav a[aria-current="page"] {
  color: var(--color-accent);
}

.nav a[aria-current="page"] {
  font-weight: 600;
}

/* ---------------------------------------------------------------------------
   Content blocks
   --------------------------------------------------------------------------- */
main {
  padding-block: var(--space-lg) var(--space-xl);
  min-height: 60vh;
}

main > h1:first-child {
  margin-block-start: 0;
}

.post-meta,
.post-list time {
  color: var(--color-muted);
  font-size: 0.9rem;
}

.post-list {
  list-style: none;
  padding: 0;
}

.post-list > li {
  padding-block: var(--space-lg);
  border-bottom: 1px solid var(--color-border);
}

.post-list > li:first-child {
  padding-block-start: var(--space-sm);
}

.post-list > li:last-child {
  border-bottom: 0;
}

.post-list h2 {
  font-size: 1.25rem;
  margin-block: 0 var(--space-sm);
}

.post-list h2 a {
  color: var(--color-text);
  text-decoration: none;
}

.post-list h2 a:hover {
  color: var(--color-accent);
  text-decoration: underline;
}

/* Teaser keeps body colour; only the byline/date recede. */
.post-list-excerpt {
  margin-block: 0 var(--space-sm);
}

.post-list .post-meta {
  margin-block: 0;
}

/* ---------------------------------------------------------------------------
   Paper list
   --------------------------------------------------------------------------- */
.year-tabs {
  margin-block-end: var(--space-lg);
  border-bottom: 1px solid var(--color-border);
}

.year-tabs ul {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-xs);
  list-style: none;
  margin: 0;
  padding: 0;
}

.year-tabs a {
  display: block;
  padding: var(--space-sm) var(--space-md);
  color: var(--color-muted);
  text-decoration: none;
  border-bottom: 2px solid transparent;
}

.year-tabs a:hover {
  color: var(--color-accent);
}

.year-tabs a[aria-current="page"] {
  color: var(--color-text);
  font-weight: 600;
  border-bottom-color: var(--color-accent);
}

.paper-list {
  list-style: none;
  padding: 0;
}

.paper-list > li {
  padding-block: var(--space-md);
}

.paper-list > li + li {
  border-top: 1px solid var(--color-border);
}

.paper-list h2 {
  font-size: 1.0625rem;
  font-weight: 600;
  margin-block: 0 var(--space-xs);
}

.paper-list h2 a {
  color: var(--color-text);
  text-decoration: none;
}

.paper-list h2 a:hover {
  color: var(--color-accent);
  text-decoration: underline;
}

.paper-authors {
  margin-block: 0 var(--space-xs);
}

.paper-meta {
  color: var(--color-muted);
  font-size: 0.9rem;
  margin-block: 0;
}

.paper-abstract {
  margin-block-start: var(--space-sm);
  font-size: 0.95rem;
}

.paper-abstract summary {
  cursor: pointer;
  color: var(--color-muted);
}

.paper-abstract summary:hover {
  color: var(--color-accent);
}

.paper-abstract p {
  margin-block: var(--space-sm) 0;
  color: var(--color-muted);
}

/* Wide display maths scrolls inside its own box rather than widening the page. */
.katex-display {
  overflow-x: auto;
  overflow-y: hidden;
  padding-block: var(--space-xs);
}

/* Shown only if KaTeX cannot parse a fragment; keeps the source visible. */
.tex-raw {
  font-family: var(--font-mono);
  font-size: 0.9em;
}

.back-link {
  margin-block-start: var(--space-xl);
}

/* ---------------------------------------------------------------------------
   Footer
   --------------------------------------------------------------------------- */
.site-footer {
  border-top: 1px solid var(--color-border);
  background: var(--color-surface);
  padding-block: var(--space-lg);
  color: var(--color-muted);
  font-size: 0.9rem;
}

.site-footer p {
  margin: 0;
}