* { box-sizing: border-box; }

html, body {
  margin: 0;
  min-height: 100%;
  background: #081525;
  color: #eaf4ff;
  font-family: Arial, Helvetica, sans-serif;
}

.lesson {
  max-width: 1050px;
  margin: 20px auto;
  padding: 22px;
  background: #10233a;
  border: 1px solid #25465f;
  border-radius: 18px;
}

h1 {
  text-align: center;
  margin: 8px 0;
  font-size: 30px;
}

.subtitle {
  text-align: center;
  color: #c0d6e6;
  line-height: 1.5;
  margin-bottom: 18px;
}

.scene {
  background: radial-gradient(ellipse at 50% 30%, #1a3651, #091a2d 75%);
  border: 1px solid #35546c;
  border-radius: 14px;
  overflow: hidden;
}

svg {
  width: 100%;
  display: block;
  touch-action: none;
}

.diagramLabel {
  font: 19px Arial, Helvetica, sans-serif;
  fill: #e5f0fb;
}

#targetRing {
  pointer-events: none;
}

#incidencePoint {
  cursor: pointer;
}

#dragHandle {
  cursor: grab;
  touch-action: none;
}

.controls, .levelControl {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin: 16px 0;
}

button {
  padding: 12px 17px;
  border: 0;
  border-radius: 9px;
  background: #19b7ca;
  color: #061827;
  font-size: 14px;
  font-weight: bold;
  cursor: pointer;
}

button:disabled {
  opacity: .4;
  cursor: not-allowed;
}

button.secondary {
  background: #28455e;
  color: #edf8ff;
}

button.level {
  background: #243d55;
  color: #d6e7f5;
}

button.level.active {
  background: #19b7ca;
  color: #061827;
}

.angleControl {
  background: #172e47;
  padding: 16px;
  border-radius: 10px;
}

.angleControl label {
  display: flex;
  justify-content: space-between;
  gap: 12px;
}

.angleControl strong {
  color: #ffd15c;
}

input[type="range"] {
  width: 100%;
  margin: 18px 0 8px;
  accent-color: #19b7ca;
}

input:disabled {
  opacity: .35;
}

.hint {
  font-size: 13px;
  color: #a7c4d7;
}

.feedback {
  background: #172e47;
  border-left: 4px solid #19b7ca;
  border-radius: 4px;
  padding: 15px;
  line-height: 1.6;
  min-height: 54px;
}

.feedback.success {
  border-left-color: #57e7a1;
  color: #a6f4cc;
}

.feedback.error {
  border-left-color: #ffbd63;
  color: #ffe0ac;
}

@media (max-width: 600px) {
  .lesson {
    margin: 0;
    padding: 12px;
    border-radius: 0;
  }

  h1 { font-size: 24px; }
  button { flex: 1; }
}