:root {
  --bg-start: #f4f6fb;
  --bg-end: #e7edf8;
  --surface: #ffffff;
  --surface-soft: #f7f9fc;
  --text: #1f2937;
  --text-muted: #4b5563;
  --primary: #111827;
  --primary-soft: #1f2a44;
  --accent: #f4b400;
  --link: #2f5ecc;
  --link-hover: #24489e;
  --border: #d9e1ec;
  --shadow: 0 10px 24px rgba(15, 23, 42, 0.08);
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: "Rubik", sans-serif;
  line-height: 1.6;
  color: var(--text);
  background: linear-gradient(120deg, var(--bg-start) 0%, var(--bg-end) 100%);
  min-height: 100vh;
}

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

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

header {
  background-color: var(--primary);
  color: #fff;
  padding: 1rem clamp(1rem, 3vw, 2rem);
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 1rem;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.22);
}

header .logo {
  font-size: 1.8rem;
  font-weight: 700;
  letter-spacing: 1px;
}

nav ul {
  list-style: none;
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.8rem;
}

nav ul li {
  margin: 0;
}

nav ul li a {
  color: #fff;
  text-decoration: none;
  font-weight: 500;
  font-size: 0.98rem;
  border-radius: 999px;
  padding: 0.35rem 0.72rem;
  transition: color 0.2s ease, background-color 0.2s ease;
}

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

main {
  max-width: 1100px;
  margin: 0 auto;
  padding: clamp(1.2rem, 3vw, 2.3rem) 1rem;
}

h1,
h2 {
  margin-bottom: 1rem;
  color: var(--primary-soft);
  line-height: 1.3;
}

p + p {
  margin-top: 0.9rem;
}

.content-box,
.about-section,
.papers,
.paper-card {
  background: var(--surface);
  border-radius: 12px;
  box-shadow: var(--shadow);
}

.content-box,
.about-section,
.papers {
  padding: clamp(1.2rem, 2vw, 2rem);
  margin-bottom: 1.4rem;
}

.hero {
  background: linear-gradient(135deg, #3b5bcc 0%, #22418d 100%);
  border-radius: 16px;
  color: #fff;
  text-align: center;
  padding: clamp(2.5rem, 6vw, 4rem) clamp(1rem, 3vw, 2rem);
  margin-bottom: 2rem;
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: "";
  position: absolute;
  inset: 0;
  background:
    radial-gradient(circle at 20% 20%, rgba(255, 255, 255, 0.25), transparent 40%),
    radial-gradient(circle at 80% 70%, rgba(255, 255, 255, 0.22), transparent 44%);
  z-index: 0;
}

.hero-content {
  position: relative;
  z-index: 1;
}

.hero h1 {
  font-size: clamp(1.9rem, 4vw, 2.6rem);
  margin-bottom: 0.8rem;
  color: #fff;
}

.hero p {
  font-size: 1.03rem;
  max-width: 760px;
  margin: 0 auto 1.6rem;
  color: #f9fbff;
}

.hero a,
.btn {
  display: inline-block;
  padding: 0.72rem 1.2rem;
  border-radius: 8px;
  text-decoration: none;
  font-size: 0.98rem;
  font-weight: 600;
  transition: transform 0.15s ease, box-shadow 0.15s ease, background-color 0.2s ease;
}

.hero a {
  background: var(--accent);
  color: var(--primary);
}

.hero a:hover,
.btn:hover {
  transform: translateY(-1px);
  box-shadow: 0 5px 14px rgba(15, 23, 42, 0.17);
}

.papers h2 {
  margin-bottom: 1.3rem;
}

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

.paper-list li {
  padding: 0.9rem 0;
  border-bottom: 1px solid var(--border);
}

.paper-list li:last-child {
  border-bottom: none;
}

.paper-list li a {
  text-decoration: none;
  font-weight: 600;
  font-size: 1.06rem;
}

.paper-meta {
  font-size: 0.89rem;
  color: var(--text-muted);
  margin-top: 0.32rem;
}

.library-container {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 1rem;
  margin-top: 1rem;
}

.paper-card {
  padding: 1.2rem;
  border: 1px solid #eef2f8;
  transition: transform 0.15s ease, box-shadow 0.2s ease;
}

.paper-card:hover {
  transform: translateY(-2px);
  box-shadow: 0 12px 24px rgba(15, 23, 42, 0.1);
}

.paper-card h3 {
  margin-bottom: 0.6rem;
  font-size: 1.1rem;
  color: #27408f;
}

.paper-card p {
  color: var(--text-muted);
  margin-bottom: 0.9rem;
}

.team-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1rem;
  margin-top: 1.4rem;
}

.team-member {
  background: var(--surface-soft);
  border: 1px solid #ebeff6;
  border-radius: 10px;
  padding: 1rem;
  text-align: center;
}

.avatar-letter {
  width: 74px;
  height: 74px;
  margin: 0 auto 0.8rem;
  border-radius: 50%;
  background: linear-gradient(135deg, #365ac3, #2a458c);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1rem;
  font-weight: 700;
  color: #fff;
  letter-spacing: 0.5px;
}

.team-member h3 {
  margin-bottom: 0.3rem;
  font-size: 1rem;
  color: #264186;
}

.team-member p {
  font-size: 0.9rem;
  color: var(--text-muted);
}

.sale-box {
  background: #f8fbff;
  border: 1px solid #d6e4fa;
  border-radius: 10px;
  padding: 1rem;
  margin-top: 1rem;
}

.sale-box ul {
  margin-left: 1.2rem;
  margin-top: 0.7rem;
}

.sale-box li + li {
  margin-top: 0.3rem;
}

.list-disc {
  list-style: disc;
  margin-left: 1.35rem;
  line-height: 1.65;
}

.list-disc li + li {
  margin-top: 0.28rem;
}

.contact-line {
  margin-top: 0.8rem;
  font-weight: 500;
}

.btn-primary {
  background: var(--accent);
  color: var(--primary);
}

.btn-secondary {
  background: var(--primary);
  color: #fff;
}

.btn-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.7rem;
  margin-top: 0.9rem;
}

footer {
  background: var(--primary);
  color: #fff;
  text-align: center;
  padding: 1.2rem;
  font-size: 0.92rem;
  margin-top: 1.8rem;
}

footer a {
  color: var(--accent);
  text-decoration: none;
}

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

@media (max-width: 768px) {
  nav ul {
    width: 100%;
    justify-content: flex-start;
  }

  nav ul li a {
    padding: 0.3rem 0.62rem;
  }
}