* {
  box-sizing: border-box;
}

html, body {
  height: 100%;
  margin: 0;
}

body {
  font-family: 'Courier New', Courier, monospace;
  background-image: url('background.png');
  background-size: cover;
  background-position: center;
  background-attachment: fixed;
  color: #e6eef6;
  display: flex;
  justify-content: center;
  padding-top: 60px;
}

.card {
  width: 720px;
  max-width: 92%;
  background: rgba(12, 12, 12, 0.65);
  border-radius: 12px;
  padding: 34px 48px;
  border: 1px solid rgba(255, 255, 255, 0.06);
  box-shadow: 0 10px 40px rgba(2, 6, 23, 0.7);
  backdrop-filter: blur(4px);
}

h1 {
  text-align: center;
  font-size: 28px;
  margin: 0;
}

.subtitle {
  text-align: center;
  margin: 18px 0;
  color: rgba(230, 238, 246, 0.75);
}

.freq-list {
  line-height: 1.6;
  white-space: pre;
  text-align: center;
  font-size: 18px;
}

.freq-row {
  display: block;
}

.freq-label {
  display: inline-block;
  width: 56px;
  text-align: right;
  margin-right: 8px;
}

.freq-value {
  display: inline-block;
  width: 80px;
  text-align: left;
}

.btn {
  padding: 10px 18px;
  border-radius: 6px;
  border: none;
  background: #404040;
  color: #fff;
  font-weight: 700;
  cursor: pointer;
  box-shadow: inset 0 -3px 0 rgba(0, 0, 0, 0.25);
}

.btn:active {
  transform: translateY(1px);
}

.center {
  display: flex;
  justify-content: center;
}

footer {
  margin-top: 12px;
  text-align: center;
  font-size: 13px;
  color: rgba(230, 238, 246, 0.6);
}