/* ---- base reset & background ---- */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: system-ui, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  background: linear-gradient(145deg, #f5f7fc 0%, #e9eef5 100%);
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1.5rem;
  margin: 0;
}

/* ---- wrapper card ---- */
.accordion-wrapper {
  max-width: 760px;
  width: 100%;
  background: rgba(255, 255, 255, 0.75);
  backdrop-filter: blur(4px);
  border-radius: 2rem;
  padding: 2rem 1.8rem;
  box-shadow:
    0 25px 40px -12px rgba(0, 20, 30, 0.25),
    0 8px 18px rgba(0, 0, 0, 0.05),
    inset 0 1px 0 rgba(255, 255, 255, 0.8);
  border: 1px solid rgba(255, 255, 255, 0.7);
  transition: all 0.2s ease;
}

/* optional heading */
.accordion-header {
  text-align: left;
  margin-bottom: 1.5rem;
  padding-left: 0.25rem;
}

.accordion-header h2 {
  font-size: 1.9rem;
  font-weight: 600;
  letter-spacing: -0.02em;
  color: #1e2b3c;
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

.accordion-header h2::before {
  content: "▍";
  font-size: 2rem;
  color: #2c7da0;
  font-weight: 400;
  line-height: 1;
}

/* ---- accordion list ---- */
.accordion {
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
}

/* ---- each accordion item ---- */
.accordion-item {
  background: #ffffff;
  border-radius: 1.3rem;
  box-shadow: 0 4px 12px rgba(0, 15, 30, 0.08), 0 1px 3px rgba(0, 0, 0, 0.02);
  border: 1px solid #eaf0f6;
  overflow: hidden;
  transition: box-shadow 0.2s ease, border-color 0.2s ease;
}

.accordion-item:hover {
  border-color: #cbd9e8;
  box-shadow: 0 8px 18px rgba(20, 50, 80, 0.08);
}

/* ---- trigger button ---- */
.accordion-trigger {
  width: 100%;
  background: transparent;
  border: none;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1.25rem 1.6rem;
  font-size: 1.2rem;
  font-weight: 500;
  line-height: 1.4;
  color: #1b2b3e;
  text-align: left;
  cursor: pointer;
  font-family: inherit;
  transition: background 0.2s ease, color 0.2s ease;
  outline: none;
  letter-spacing: -0.01em;
  gap: 1rem;
}

.accordion-trigger:focus-visible {
  outline: 3px solid #2c7da0;
  outline-offset: -3px;
  border-radius: 1.3rem;
}

/* ---- plus / minus icon ---- */
.accordion-icon {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  width: 28px;
  height: 28px;
  background: #eef3f9;
  border-radius: 50%;
  color: #1e4a6b;
  font-weight: 400;
  transition: all 0.25s cubic-bezier(0.2, 0.9, 0.4, 1);
  font-size: 1.3rem;
  line-height: 1;
  user-select: none;
}

.accordion-icon::before {
  content: "+";
  display: block;
  transform: translateY(-0.5px);
}

.accordion-item.active .accordion-icon {
  background: #2c7da0;
  color: white;
  transform: rotate(180deg);
}

.accordion-item.active .accordion-icon::before {
  content: "−";
}

/* ---- panel (hidden by default) ---- */
.accordion-panel {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.4s cubic-bezier(0.33, 1, 0.68, 1);
  background: #fafdff;
  border-top: 1px solid transparent;
}

.accordion-content {
  padding: 0 1.6rem 1.5rem 1.6rem;
  color: #2d3f53;
  font-size: 1.05rem;
  line-height: 1.65;
  border-top: 1px solid #e7eef7;
  margin-top: 0.2rem;
  padding-top: 1.2rem;
}

.accordion-content p {
  margin-bottom: 0.75rem;
}

.accordion-content p:last-child {
  margin-bottom: 0;
}

.accordion-item.active .accordion-trigger {
  background: #f6faff;
  color: #0f2c40;
}

.accordion-content code {
  background: #e4ecf5;
  padding: 0.2rem 0.4rem;
  border-radius: 6px;
  font-size: 0.95em;
  color: #1e4a6b;
}

/* ---- responsive ---- */
@media (max-width: 500px) {
  .accordion-wrapper {
    padding: 1.5rem 1rem;
    border-radius: 1.5rem;
  }

  .accordion-trigger {
    padding: 1rem 1.2rem;
    font-size: 1.05rem;
  }

  .accordion-content {
    padding: 0 1.2rem 1.3rem 1.2rem;
    font-size: 0.98rem;
  }

  .accordion-header h2 {
    font-size: 1.6rem;
  }

  .accordion-icon {
    width: 26px;
    height: 26px;
    font-size: 1.2rem;
  }
}