.panel-container {
  position: relative;
  width: 100%;
  max-width: 800px;
  margin: auto;
}
.chart-pane {
  display: none;
}
.chart-pane.active {
  display: block;
}
.nav-button {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  font-size: 24px;
  cursor: pointer;
  background: #f2f2f2;
  border-radius: 50%;
  padding: 8px 14px;
  box-shadow: 0 2px 5px rgba(0,0,0,0.2);
  user-select: none;
}
.nav-button:hover {
  background: #e0e0e0;
}
#prevBtn {left: -50px;}
#nextBtn {right: -50px;}