* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  background: linear-gradient(135deg, #0d1b2a 0%, #1b2838 50%, #162447 100%);
  min-height: 100vh;
  color: #333;
  display: flex;
  flex-direction: column;
}

.app-container {
  flex: 1;
  max-width: 1400px;
  margin: 0 auto;
  padding: 2rem;
  width: 100%;
}

.header {
  text-align: center;
  margin-bottom: 2rem;
}

.header h1 {
  color: white;
  font-size: 2.5rem;
  margin-bottom: 0.5rem;
  text-shadow: 2px 2px 4px rgba(0,0,0,0.3);
}

.header p {
  color: rgba(255,255,255,0.85);
  font-size: 1.1rem;
}

.main-content {
  display: grid;
  grid-template-columns: 420px 1fr;
  gap: 2rem;
}

@media (max-width: 1000px) {
  .main-content {
    grid-template-columns: 1fr;
  }
}

.left-panel, .right-panel {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.visualization-section,
.controls-section,
.sequence-section,
.state-section,
.explainer-section {
  background: white;
  border-radius: 12px;
  padding: 1.5rem;
  box-shadow: 0 4px 20px rgba(0,0,0,0.15);
}

h3 {
  font-size: 1.1rem;
  color: #333;
  margin-bottom: 1rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

/* Connection visualization */
.connection-vis {
  display: flex;
  align-items: stretch;
  gap: 0;
  min-height: 160px;
}

.endpoint {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 1rem;
  border-radius: 10px;
  min-width: 90px;
}

.client-side {
  background: linear-gradient(135deg, #d6eaf8 0%, #aed6f1 100%);
}

.server-side {
  background: linear-gradient(135deg, #d5f5e3 0%, #abebc6 100%);
}

.endpoint-label {
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  color: #555;
  margin-bottom: 0.5rem;
}

.endpoint-state {
  font-size: 1rem;
  font-weight: 700;
  padding: 0.4rem 0.8rem;
  border-radius: 6px;
  background: white;
  color: #333;
  text-align: center;
}

.endpoint-state.client_established,
.endpoint-state.server_established {
  background: #27ae60;
  color: white;
}

.endpoint-state.client_syn_sent,
.endpoint-state.server_syn_received {
  background: #f39c12;
  color: white;
}

.endpoint-state.client_fin_wait,
.endpoint-state.server_closed {
  background: #e74c3c;
  color: white;
}

.packet-lane {
  flex: 1;
  position: relative;
  min-width: 200px;
}

.packet-lane svg {
  width: 100%;
  height: 100%;
}

/* Transition buttons */
.transitions-container {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  margin-bottom: 1rem;
}

.btn-transition {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.6rem 1rem;
  border: 2px solid #e0e0e0;
  border-radius: 8px;
  background: white;
  cursor: pointer;
  transition: all 0.2s;
  text-align: left;
}

.btn-transition.enabled:hover {
  transform: translateX(4px);
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

.btn-transition.disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.trans-label {
  font-weight: 700;
  font-size: 0.9rem;
  min-width: 70px;
}

.trans-desc {
  font-size: 0.8rem;
  color: #888;
}

.control-buttons {
  display: flex;
  gap: 0.5rem;
}

.btn {
  flex: 1;
  padding: 0.7rem 1rem;
  border: none;
  border-radius: 8px;
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
}

.btn-primary {
  background: linear-gradient(135deg, #2980b9 0%, #3498db 100%);
  color: white;
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(52, 152, 219, 0.4);
}

.btn-warning {
  background: linear-gradient(135deg, #c0392b 0%, #e74c3c 100%);
  color: white;
}

.btn-warning:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(231, 76, 60, 0.4);
}

.btn-secondary {
  background: #e9ecef;
  color: #495057;
}

.btn-secondary:hover {
  background: #dee2e6;
}

/* Sequence log */
.sequence-log {
  max-height: 200px;
  overflow-y: auto;
  font-size: 0.85rem;
  line-height: 1.6;
}

.seq-entry {
  padding: 0.3rem 0.5rem;
  border-radius: 4px;
  margin-bottom: 2px;
  background: #f8f9fa;
  font-family: 'SF Mono', Monaco, monospace;
  font-size: 0.8rem;
}

.seq-entry.info {
  background: #f0fff4;
  color: #276749;
  font-family: inherit;
}

.seq-arrow {
  font-weight: 600;
}

/* State machine display */
.state-machines {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.5rem;
}

.sm-title {
  font-size: 0.85rem;
  font-weight: 600;
  color: #555;
  text-transform: uppercase;
  margin-bottom: 0.75rem;
  text-align: center;
}

.state-list {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}

.sm-state {
  padding: 0.5rem 0.75rem;
  border-radius: 6px;
  text-align: center;
  font-size: 0.85rem;
  font-weight: 500;
  background: #f0f0f0;
  color: #999;
  transition: all 0.3s;
}

.sm-state.active {
  background: linear-gradient(135deg, #3498db 0%, #2980b9 100%);
  color: white;
  font-weight: 700;
  box-shadow: 0 2px 8px rgba(52, 152, 219, 0.3);
}

/* Explainer */
.explainer-content {
  font-size: 0.9rem;
  line-height: 1.7;
  color: #555;
}

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

.explainer-content ul {
  margin: 0.75rem 0;
  padding-left: 1.5rem;
}

.explainer-content li {
  margin-bottom: 0.5rem;
}

.explainer-content strong {
  color: #333;
}