:root {
  --bg: #000000;
  --bg-dark: #111111;
  --text: #e5e7eb;
  --green: #00b400;
  --red: #dc2828;
  --orange: #ff8c00;
}
* { box-sizing: border-box }
html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: Segoe UI, Roboto, Arial, Helvetica, sans-serif;
}
.start {
  min-height: 100vh;
  display: grid;
  place-items: center;
  grid-template-rows: auto auto auto auto;
  gap: 14px;
  padding: 24px;
}
.title {
  font-size: 34px;
  color: var(--orange);
  letter-spacing: 0.5px;
}
.version {
  font-size: 16px;
  color: #bbb;
}
.start-btn {
  border: 1px solid #333;
  background: var(--bg-dark);
  color: var(--green);
  padding: 10px 18px;
  border-radius: 6px;
  cursor: pointer;
}
.start-btn:hover { border-color: #444 }
.mark {
  display: grid;
  place-items: center;
}
.plus {
  position: relative;
  width: 84px;
  height: 84px;
  filter: drop-shadow(0 0 16px rgba(255,140,0,0.3));
}
.plus::before,
.plus::after {
  content: "";
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  background: linear-gradient(135deg, #ff8c00 0%, #00b400 60%, #dc2828 100%);
  border-radius: 6px;
}
.plus::before {
  width: 20px;
  height: 84px;
}
.plus::after {
  width: 84px;
  height: 20px;
}
.app {
  max-width: 900px;
  margin: 32px auto;
  padding: 24px;
}
h1 {
  margin: 0 0 16px 0;
  color: var(--orange);
  font-weight: 600;
}
form {
  display: grid;
  gap: 12px;
}
label {
  display: grid;
  gap: 6px;
  color: var(--orange);
}
input[type="number"] {
  appearance: none;
  border: 1px solid #333;
  background: var(--bg-dark);
  color: var(--green);
  padding: 10px 12px;
  border-radius: 4px;
  outline: none;
}
input[type="number"]::placeholder {
  color: #888;
}
button {
  border: 1px solid #333;
  background: var(--bg);
  color: var(--red);
  padding: 10px 14px;
  border-radius: 4px;
  cursor: pointer;
}
button:hover {
  border-color: #444;
}
.output {
  margin-top: 18px;
  padding: 12px;
  border: 1px solid #333;
  background: var(--bg-dark);
  color: var(--green);
  min-height: 120px;
  white-space: pre-wrap;
}