/* ===== Reset & Base ===== */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --color-bg: #faf9f7;
  --color-text: #2c2c2c;
  --color-text-light: #6b6b6b;
  --color-accent: #1a4a6e;
  --color-accent-hover: #0e3350;
  --color-border: #e0ddd8;
  --color-header-bg: #ffffff;
  --font-body: "Source Serif 4", "Noto Serif JP", Georgia, serif;
  --font-heading: "Source Serif 4", "Noto Serif JP", Georgia, serif;
  --font-nav: "Source Sans 3", "Noto Sans JP", Helvetica, Arial, sans-serif;
  --max-width: 920px;
}

html {
  font-size: 17px;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-body);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.72;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ===== Typography (Google Fonts) ===== */
@import url('https://fonts.googleapis.com/css2?family=Source+Serif+4:ital,wght@0,400;0,600;0,700;1,400&family=Source+Sans+3:wght@400;500;600&family=Noto+Serif+JP:wght@400;600&family=Noto+Sans+JP:wght@400;500&display=swap');

/* ===== Header ===== */
header {
  background: var(--color-header-bg);
  border-bottom: 1px solid var(--color-border);
  position: sticky;
  top: 0;
  z-index: 100;
}

.header-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 1.1rem 1.5rem;
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 1.5rem;
}

.site-title {
  font-family: var(--font-heading);
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--color-text);
  text-decoration: none;
  letter-spacing: -0.01em;
  white-space: nowrap;
}

nav {
  display: flex;
  gap: 1.6rem;
}

nav a {
  font-family: var(--font-nav);
  font-size: 0.92rem;
  font-weight: 500;
  color: var(--color-text-light);
  text-decoration: none;
  padding-bottom: 2px;
  border-bottom: 2px solid transparent;
  transition: color 0.2s, border-color 0.2s;
}

nav a:hover {
  color: var(--color-text);
}

nav a.active {
  color: var(--color-accent);
  border-bottom-color: var(--color-accent);
}

/* ===== Main ===== */
main {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 2.5rem 1.5rem 4rem;
  flex: 1;
  width: 100%;
}

h1 {
  font-family: var(--font-heading);
  font-size: 1.65rem;
  font-weight: 700;
  margin-bottom: 1.4rem;
  letter-spacing: -0.015em;
  color: var(--color-text);
}

h2 {
  font-family: var(--font-heading);
  font-size: 1.15rem;
  font-weight: 600;
  margin-top: 2.2rem;
  margin-bottom: 0.8rem;
  color: var(--color-text);
}

p {
  margin-bottom: 1rem;
}

a {
  color: var(--color-accent);
  text-decoration: none;
  transition: color 0.15s;
}

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

/* ===== About Page Layout ===== */
.about-layout {
  display: flex;
  gap: 2.4rem;
  align-items: flex-start;
}

.portrait-col {
  flex-shrink: 0;
}

.portrait-placeholder {
  width: 220px;
  background: var(--color-border);
  border-radius: 4px;
  overflow: hidden;
}

.portrait-placeholder img {
  width: 100%;
  height: auto;
  display: block;
  border-radius: 4px;
}

.bio-col {
  flex: 1;
  min-width: 0;
}

/* ===== Research Page ===== */
.research-section {
  margin-bottom: 1.5rem;
}

.pub-item {
  margin-bottom: 1.3rem;
  padding-left: 0.6rem;
  border-left: 3px solid var(--color-border);
}

.pub-title {
  font-weight: 600;
  margin-bottom: 0.15rem;
  line-height: 1.45;
}

.pub-meta {
  font-size: 0.9rem;
  color: var(--color-text-light);
  margin-bottom: 0.2rem;
}

.pub-links {
  font-family: var(--font-nav);
  font-size: 0.85rem;
  margin-bottom: 0;
}

.pub-links a {
  font-weight: 500;
}

/* ===== Teaching Page ===== */
.teaching-section {
  margin-bottom: 2.5rem;
}

.teaching-section h2 {
  font-size: 1.25rem;
  font-weight: 700;
  margin-top: 2.5rem;
  margin-bottom: 0.5rem;
  padding-bottom: 0.45rem;
  border-bottom: 2px solid var(--color-border);
  letter-spacing: -0.01em;
}

.course-item {
  margin-bottom: 1.2rem;
  padding-left: 0.6rem;
}

.course-title {
  font-weight: 600;
  font-size: 0.95rem;
  margin-bottom: 0.1rem;
}

.course-meta {
  font-family: var(--font-body);
  font-size: 0.9rem;
  color: var(--color-text-light);
  margin-bottom: 0.25rem;
  font-style: italic;
}

.course-desc {
  font-size: 0.95rem;
}

/* ===== Footer ===== */
footer {
  border-top: 1px solid var(--color-border);
  padding: 1.5rem;
  text-align: center;
  font-family: var(--font-nav);
  font-size: 0.8rem;
  color: var(--color-text-light);
}

/* ===== Responsive ===== */
@media (max-width: 600px) {
  html {
    font-size: 16px;
  }

  .header-inner {
    flex-direction: column;
    gap: 0.6rem;
    padding: 0.9rem 1.2rem;
  }

  nav {
    gap: 1.2rem;
  }

  .about-layout {
    flex-direction: column;
    gap: 1.5rem;
  }

  .portrait-placeholder {
    width: 130px;
    height: 165px;
  }

  main {
    padding: 1.8rem 1.2rem 3rem;
  }
}