* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  font-family: 'Poppins', sans-serif;
}

body {
  background-color: var(--bg-color);
  display: flex;
  flex-direction: column;
  height: 100vh;
  overflow: hidden;
  transition: background-color 0.3s ease, color 0.3s ease;
}

/* header */
header {
  background: var(--card-bg);
  color: var(--text-main);
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  height: 100px;
  box-shadow: 0 4px 10px var(--shadow-color);
  transition: background-color 0.3s ease, box-shadow 0.3s ease;
}

header h1 {
  margin: 0;
  font-size: 2.2rem;
  font-weight: 600;
}

header p {
  margin-top: 0.5rem;
  font-size: 1.1rem;
  color: var(--text-muted);
}

/* main layout */
.main-layout {
  display: flex;
  gap: 1.5rem;
  flex: 1;
  align-items: stretch;
  padding: 1rem 2rem;
  color: var(--text-main);
  max-width: 1200px;
  margin: 10px auto;
  width: 100%;
}

/* layout article */
.main-layout article {
  flex: 3;
  display: flex;
  flex-direction: column;
  border-radius: 12px;
  background: var(--card-bg);
  padding: 2rem;
  box-shadow: 0 4px 15px var(--shadow-color);
  line-height: 1.6;
  transition: background-color 0.3s ease, box-shadow 0.3s ease;
}

.main-layout article p {
  color: var(--text-main);
  font-size: 1.05rem;
}

/* layout aside */
.main-layout aside {
  flex: 1;
  border-radius: 12px;
  background: var(--card-bg);
  padding: 1.5rem;
  box-shadow: 0 4px 15px var(--shadow-color);
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  transition: background-color 0.3s ease, box-shadow 0.3s ease;
}

.main-layout aside p {
  color: var(--text-main);
  font-size: 1rem;
}

/* hyperlink in aside */
aside a {
  color: var(--accent);
  text-decoration: none;
  font-weight: 500;
  transition: color 0.3s;
}

aside a:hover {
  color: var(--accent-hover);
}

.openbtn {
  font-size: 16px;
  font-weight: 500;
  cursor: pointer;
  background-color: var(--accent);
  color: #fff;
  padding: 12px 20px;
  border: none;
  border-radius: 8px;
  transition: all 0.3s ease;
  margin-top: 1.5rem;
  box-shadow: 0 4px 6px var(--shadow-hover);
}

.openbtn:hover {
  background-color: var(--accent-hover);
  transform: translateY(-2px);
  box-shadow: 0 6px 12px var(--shadow-hover);
}

/* footer */
footer {
  width: 100%;
  background-color: var(--footer-bg);
  color: var(--text-muted);
  text-align: center;
  height: 60px;
  display: flex;
  justify-content: center;
  align-items: center;
  margin-top: auto;
  transition: background-color 0.3s ease;
}

/* Mobile Responsiveness */
@media (max-width: 768px) {
  body {
    height: auto;
    overflow-y: auto;
  }

  .main-layout {
    flex-direction: column;
    padding: 1rem;
    gap: 1.5rem;
  }

  header h1 {
    font-size: 1.8rem;
  }
}