* {
  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;
}

header {
  text-align: center;
}

h1 {
  margin: 10px 0 6px;
  font-size: 30px;
  color: #ffffff;
}

header p {
  margin: 0 0 18px;
  color: #b7cde0;
}

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

svg {
  display: block;
  width: 100%;
  height: auto;
  max-height: 510px;
}

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

.angle {
  font: bold 24px Arial, Helvetica, sans-serif;
}

.controls {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
  margin: 18px 0;
}

button {
  background: #19b7ca;
  border: 0;
  border-radius: 9px;
  padding: 13px 20px;
  font-size: 15px;
  font-weight: bold;
  color: #051827;
  cursor: pointer;
}

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

.angleControl {
  flex: 1;
  min-width: 210px;
  color: #d6e8f7;
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
}

.angleControl strong {
  color: #ffd15c;
}

input[type="range"] {
  width: 100%;
  accent-color: #19b7ca;
  cursor: pointer;
}

.readout {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
}

.readout span {
  flex: 1;
  min-width: 200px;
  padding: 14px;
  background: #172e47;
  border-radius: 9px;
  display: flex;
  justify-content: space-between;
  gap: 12px;
}

.readout b {
  color: #fbd475;
}

.explanation {
  line-height: 1.55;
  color: #d3e8f5;
}

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

  h1 {
    font-size: 24px;
  }

  .controls button {
    flex: 1;
  }
}