:root{
  /* default value (each page may override) */
  --page-pad: 40px;

  /* EPFL palette */
  --epfl-red: #FF0000;
  --epfl-red-hover: #CC0000;

  --text: #1d1d1b;
  --text-muted: #5c5c5c;
  --text-subtle: #8a8a8a;

  --bg: #ffffff;
  --bg-soft: #f5f5f5;

  --border-light: #e5e5e5;
  --border: #cccccc;
  --border-strong: #999999;
}

*{ box-sizing: border-box; }

body{
  margin: 0;
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  padding-top: 12px; /* space above the header */
}

/* Shared HEADER + NAV */
.site-header{
  background: var(--bg);
  border-bottom: 1px solid var(--border-light);
}

.header-row{
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding-top: 14px;
  padding-bottom: 14px;
}

.epfl-logo{
  display: flex;
  align-items: center;
  line-height: 0;
}

.epfl-logo img{
  display: block;
  height: 53px;
  width: auto;
}

.top-nav{
  display: flex;
  align-items: center;
  gap: 10px;
}

.nav-btn{
  display: inline-block;
  padding: 4px 10px;
  font-size: 0.85em;
  color: var(--text);
  text-decoration: none;
  border: 1px solid var(--border);
  border-radius: 4px;
  background: transparent;
  transition: background-color 0.15s ease, color 0.15s ease, border-color 0.15s ease;
}

.nav-btn:hover{
  background: var(--bg-soft);
  border-color: var(--border-strong);
}

.nav-btn.active{
  background: var(--epfl-red);
  border-color: var(--epfl-red);
  color: #ffffff;
}

.nav-btn.active:hover{
  background: var(--epfl-red-hover);
  border-color: var(--epfl-red-hover);
}