:root {
  --primary: #17365d;
  --secondary: #285985;
  --background: #f5f7fa;
  --text: #222222;
  --muted: #5f6670;
  --border: #d9dee5;
  --white: #ffffff;
  --link: #155fa0;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--background);
  color: var(--text);
  font-family: Arial, Helvetica, sans-serif;
  font-size: 17px;
  line-height: 1.65;
}

a {
  color: var(--link);
}

a:hover {
  text-decoration-thickness: 2px;
}

/* 顶部标题区域 */

header {
  background: var(--primary);
  color: var(--white);
  padding: 55px 20px 45px;
  text-align: center;
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 28px;
}

.header-logo {
  display: block;
  width: 160px;
  max-width: 35vw;
  height: auto;
  margin: 0;
}

header h1 {
  margin: 0;
  font-size: 2em;
  letter-spacing: 0.02em;
}

.header-title {
  text-align: left;
  line-height: 1.1;
}

.header-title span {
  display: block;
}

header p {
  max-width: 800px;
  margin: 15px auto 0;
  font-size: 1.15rem;
  opacity: 0.95;
}

/* 导航栏 */

nav {
  position: sticky;
  top: 0;
  z-index: 10;
  background: var(--secondary);
  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.18);
}

.nav-inner {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 28px;

  max-width: 1050px;
  margin: 0 auto;
  padding: 12px 20px;
}

nav a {
  display: inline-block;
  margin: 4px 15px;
  color: var(--white);
  font-weight: 600;
  text-decoration: none;
}

nav a:hover {
  text-decoration: underline;
}

/* 页面主体 */

main {
  max-width: 1000px;
  min-height: 520px;
  margin: 35px auto;
  padding: 0 20px;
}

section {
  margin-bottom: 28px;
  padding: 30px;
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: 8px;
  box-shadow: 0 2px 7px rgba(0, 0, 0, 0.05);
}

h2 {
  margin-top: 0;
  padding-bottom: 8px;
  color: var(--primary);
  font-size: 1.8rem;
  border-bottom: 2px solid var(--border);
}

h3,
h4 {
  color: var(--primary);
}

/* 报告信息 */

.registration-notice {
  margin: 0 0 18px;
}

.talk-separator {
  margin: 0 0 24px;
  border: 0;
  border-top: 1px solid var(--border);
}

.talk-card {
  margin-top: 20px;
  padding: 22px;
  border: 1px solid var(--border);
  border-radius: 6px;
}

.talk-card h3 {
  margin-top: 0;
  margin-bottom: 10px;
  font-size: 1.3rem;
}

.talk-card .talk-label {
  margin-right: 0.4em;
  color: var(--muted);
  font-size: inherit;
  font-weight: 700;
  letter-spacing: 0.02em;
}

.speaker {
  margin: 0 0 8px;
  font-size: 1.2rem;
}

.speaker-name {
  font-weight: 700;
}

.speaker-affiliation {
  color: var(--muted);
  font-size: 0.875em;
}

.talk-detail {
  margin: 2px 0;
  font-size: 1.05rem;
}

.talk-abstract-heading {
  margin: 24px 0 8px;
  font-size: 1em;
  line-height: 1.3;
}

.upcoming-talk-card > h3,
.upcoming-talk-card > .speaker,
.upcoming-talk-card > .talk-detail,
.upcoming-talk-card > .talk-abstract-heading {
  margin: 0 0 12px;
}

.upcoming-talk-card {
  margin-top: 0;
}

.upcoming-talk-card + .upcoming-talk-card {
  margin-top: 24px;
}

.talk-card .abstract {
  margin-top: 0;
}

.talk-card .abstract p {
  margin: 0 0 1em;
}

.talk-card .abstract p:last-child {
  margin-bottom: 0;
}

.institution,
.time,
.location {
  color: var(--muted);
}

.abstract,
.biography {
  margin-top: 20px;
}

/* 提示框 */

.notice {
  padding: 18px;
  background: #eef5fb;
  border-left: 5px solid var(--secondary);
  border-radius: 3px;
}

/* 按钮 */

.button {
  display: inline-block;
  margin-top: 10px;
  margin-right: 8px;
  padding: 9px 16px;
  background: var(--primary);
  color: var(--white);
  border-radius: 4px;
  font-weight: 600;
  text-decoration: none;
}

.button:hover {
  background: var(--secondary);
}

/* 组织者列表 */

.organizer-list {
  padding-left: 22px;
}

.organizer-list li {
  margin-bottom: 18px;
}

/* 页脚 */

footer {
  margin-top: 45px;
  padding: 28px 20px;
  background: var(--primary);
  color: var(--white);
  text-align: center;
}

footer p {
  margin: 0;
}

footer a {
  color: var(--white);
}

/* 移动端 */

@media (max-width: 700px) {
  header h1 {
    font-size: 1.25rem;
  }

  .header-inner {
    gap: 16px;
  }

  header {
    padding: 40px 20px 32px;
  }

  nav {
    position: static;
  }

  nav a {
    display: block;
    margin: 8px;
  }

  section {
    padding: 22px;
  }
}