body {
  background: #fff;
  color: #222;
  font-family: Arial, Helvetica, sans-serif;
  margin: 0;
  padding: 0;
}
#container {
  display: flex;
  min-height: 100vh;
}
#sidebar {
  width: 350px;
  min-height: 100vh;
  background: #222;
  color: #fff;
  padding: 0;
  border-right: 2px solid #00c853;
  box-sizing: border-box;
  overflow-y: auto;
  position: fixed;
  left: 0;
  top: 0;
  bottom: 0;
}
.logo {
  font-size: 1.2rem;
  font-weight: bold;
  color: #00c853;
  padding: 1.2rem 1.5rem 1rem 1.5rem;
  border-bottom: 1px solid #333;
  background: #181818;
  letter-spacing: 1px;
  text-align: center;
}
#tree {
  list-style: none;
  margin: 0;
  padding: 1rem 0.5rem 2rem 0.5rem;
}
.tree-category {
  margin-bottom: 0.5rem;
}
.tree-label {
  font-weight: 600;
  color: #00c853;
  cursor: pointer;
  padding: 0.3rem 0.7rem 0.3rem 0.2rem;
  border-radius: 4px;
  display: flex;
  align-items: center;
  user-select: none;
  font-size: 1.05rem;
}
.tree-label:hover {
  background: #333;
}
.triangle {
  display: inline-block;
  margin-right: 7px;
  width: 0;
  height: 0;
  border-top: 6px solid transparent;
  border-bottom: 6px solid transparent;
  border-left: 8px solid #00c853;
  transition: transform 0.2s;
}
.triangle.down {
  transform: rotate(90deg);
}
.tree-items {
  margin-left: 1.2rem;
  margin-top: 0.2rem;
  padding-left: 0.5rem;
  border-left: 2px solid #00c85333;
  display: none;
}
.tree-category.open > .tree-items {
  display: block;
}
.tree-item {
  color: #fff;
  padding: 0.18rem 0.7rem 0.18rem 1.2rem;
  border-radius: 3px;
  cursor: pointer;
  font-size: 0.98rem;
  margin-bottom: 0.1rem;
  transition: background 0.15s, color 0.15s;
  position: relative;
}
.tree-item:hover {
  background: #00c853;
  color: #181818;
}
#main-content {
  flex: 1;
  padding: 2.5rem 2rem 2rem 2rem;
  background: #fff;
  min-height: 100vh;
}
#main-content h1 {
  color: #00c853;
  font-size: 2rem;
  margin-top: 0;
}
footer {
  text-align: center;
  padding: 1rem;
  background: #222;
  color: #888;
  font-size: 0.9rem;
  border-top: 1px solid #333;
  position: fixed;
  left: 0;
  bottom: 0;
  width: 350px;
  z-index: 10;
}
footer a {
  color: #00c853;
  text-decoration: none;
}
@media (max-width: 600px) {
  #sidebar, footer {
    width: 100vw;
    min-width: unset;
    position: static;
  }
}