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

/* Body */
body {
  font-family: 'Bitter', serif;
  background-color: #D3D3D3;
}

/* Navigation Bar */
nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 15px 40px;
  position: fixed;
  width: 100%;
  top: 0;
  background-color: rgba(255, 235, 59, 0.95);
  z-index: 1000;
  box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

/* Logo / Home link */
.nav-left a {
  font-size: 1.6rem;
  font-weight: 700;
  text-decoration: none;
  color: #ff4900;
}

/* Navigation tabs */
.nav-right {
  display: flex;
  gap: 40px;
  align-items: center;
}

.nav-right a {
  text-decoration: none;
  color: #000;
  font-weight: 400;
  font-size: 1.1rem;
  transition: color 0.3s;
}

.nav-right a:hover {
  color: #333;
}

/* Hamburger Menu */
.hamburger {
  display: none; /* hidden on desktop */
  flex-direction: column;
  cursor: pointer;
  gap: 5px;
}

.hamburger .bar {
  width: 25px;
  height: 3px;
  background-color: #000;
  transition: 0.3s;
}

/* Hero Section */
main {
  margin-top: 80px;
}

.hero {
  position: relative;
  width: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 40px;
}

.hero-image {
  width: 100%;
  height: auto;       /* scale height proportionally */
  display: block;
}

.center-text {
  position: fixed;    /* stays centered in viewport */
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  text-align: center;
  color: #EFFD5F;
  max-width: 90%;
  z-index: 10;
}

.center-text h1 {
  font-size: 3rem;
  font-weight: 700;
  margin-bottom: 15px;
}

.center-text p {
  font-size: 1.5rem;
  font-weight: 400;
}

/* Mathematics content box */
.content-box {
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: min(800px, 90%);
  background: rgba(255, 235, 59, 0.95);
  padding: 30px 40px;
  border-radius: 12px;
  box-shadow: 0 10px 30px rgba(0,0,0,0.2);
  z-index: 20;
  max-height: 70vh;      /* visible height */
  overflow-y: auto;      /* internal scrolling */
  scroll-behavior: smooth;
}

.content-box::-webkit-scrollbar {
  width: 8px;
}

.content-box::-webkit-scrollbar-thumb {
  background: rgba(0,0,0,0.25);
  border-radius: 4px;
}

.content-box h1 {
  font-size: 2.4rem;
  margin-bottom: 20px;
  color: #ff4900;
}

/* Paper list */
.paper-list {
  list-style: none;
}

.paper-list li {
  margin-bottom: 15px;
  font-size: 1.2rem;
}

.paper-list a {
  text-decoration: none;
  color: #000;
  font-weight: 500;
}

.paper-title {
  font-weight: 500;
  font-size: 1.2rem;
  color: #000;
}

.paper-list a:hover {
  text-decoration: underline;
}

.paper-meta {
  color: #555;
  font-size: 1rem;
  font-style: italic;
  margin-left: 8px;
}

.paper-desc {
  margin-top: 5px;
  margin-left: 5px;
  font-size: 1rem;
  color: #444;
  line-height: 1.4;
}

@media (max-width: 768px) {
  /* Nav */
  .nav-right {
    position: absolute;
    top: 65px;
    right: 0;
    background-color: rgba(255,235,59,0.95);
    flex-direction: column;
    width: 100%;
    text-align: center;
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.3s ease;
  }

  .nav-right.active {
    max-height: 500px;
  }

  .nav-right a {
    padding: 15px 0;
    font-size: 1.3rem;
    display: block;
  }

  .hamburger {
    display: flex;
  }

  /* Center text */
  .center-text h1 { font-size: 2rem; }
  .center-text p { font-size: 1rem; }

  /* Mathematics box */
  .content-box {
    padding: 20px;
  }

  .content-box h1 {
    font-size: 1.8rem;
  }

  .paper-list a,
  .paper-title {
    font-size: 1.05rem;
  }

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