:root {
  --bg-start: #f4f8ff;
  --bg-end: #e8fff6;
  --panel: #ffffff;
  --text: #11223a;
  --muted: #57718e;
  --line: #d7e4f3;
  --accent: #1f9d72;
  --accent-dark: #157454;
  --tip-btn: #f4f7fb;
  --tip-btn-active: #d3f8ea;
  --shadow: 0 12px 28px rgba(17, 34, 58, 0.12);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Avenir Next", "Segoe UI", sans-serif;
  color: var(--text);
  background: linear-gradient(140deg, var(--bg-start), var(--bg-end));
}

.app-shell {
  display: grid;
  place-items: center;
  padding: 1rem;
}

.calculator {
  width: min(100%, 36rem);
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 1rem;
  box-shadow: var(--shadow);
  padding: 1.2rem;
}

h1 {
  margin: 0;
  font-size: 1.6rem;
  line-height: 1.2;
}

.subtitle {
  margin: 0.35rem 0 1.1rem;
  color: var(--muted);
}

#tip-form {
  display: grid;
  gap: 1rem;
}

.block {
  display: grid;
  gap: 0.6rem;
}

.block h2,
.results h2 {
  margin: 0;
  font-size: 1rem;
}

input {
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 0.75rem;
  padding: 0.85rem 0.9rem;
  font-size: 1rem;
  color: var(--text);
  background: #fff;
}

input:focus,
.tip-btn:focus,
.reset-btn:focus {
  outline: 3px solid rgba(31, 157, 114, 0.25);
  outline-offset: 2px;
}

.input-wrap {
  display: grid;
  grid-template-columns: auto 1fr;
  align-items: center;
  border: 1px solid var(--line);
  border-radius: 0.75rem;
  padding-left: 0.85rem;
}

.input-wrap:focus-within {
  outline: 3px solid rgba(31, 157, 114, 0.25);
  outline-offset: 2px;
}

.input-wrap span {
  font-weight: 700;
}

.input-wrap input {
  border: none;
  outline: none;
  padding-left: 0.35rem;
}

.tip-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.55rem;
}

.tip-btn {
  border: 1px solid var(--line);
  border-radius: 0.75rem;
  background: var(--tip-btn);
  font-size: 1rem;
  font-weight: 700;
  color: var(--text);
  min-height: 3rem;
  cursor: pointer;
}

.tip-btn.is-active {
  background: var(--tip-btn-active);
  border-color: var(--accent);
  color: var(--accent-dark);
}

.tip-custom {
  grid-column: span 2;
}

.custom-label {
  font-size: 0.9rem;
  color: var(--muted);
}

#custom-tip:disabled {
  background: #f6f9fc;
  color: #8ba0b8;
}

.results {
  background: linear-gradient(180deg, #f6fffb, #ebfff7);
  border: 1px solid #bdeedb;
  border-radius: 0.9rem;
  padding: 0.9rem;
}

.results dl {
  margin: 0.6rem 0 0;
  display: grid;
  gap: 0.55rem;
}

.result-row {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 1rem;
}

.result-row dt {
  color: var(--muted);
}

.result-row dd {
  margin: 0;
  font-size: 1.1rem;
  font-weight: 700;
}

.result-row.highlight dd {
  font-size: 1.45rem;
  color: var(--accent-dark);
}

.reset-btn {
  border: none;
  border-radius: 0.75rem;
  background: var(--accent);
  color: #fff;
  font-size: 1rem;
  font-weight: 700;
  min-height: 3rem;
  cursor: pointer;
}

.reset-btn:hover {
  background: var(--accent-dark);
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

@media (min-width: 640px) {
  .calculator {
    padding: 1.6rem;
  }

  .tip-grid {
    grid-template-columns: repeat(5, minmax(0, 1fr));
  }

  .tip-custom {
    grid-column: auto;
  }
}