@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&display=swap');

/* ───── Design Tokens ───── */
:root {
  --bg:           #f0f1f5;
  --card-bg:      #ffffff;
  --card-border:  #e4e6ee;
  --card-shadow:  0 4px 6px -1px rgba(0,0,0,0.07), 0 12px 40px -8px rgba(0,0,0,0.1);
  --input-bg:     #f7f8fc;
  --input-border: #dde0ea;
  --input-focus:  rgba(255, 140, 0, 0.25);
  --accent:       #ff8c00;
  --accent-2:     #ff4500;
  --accent-light: #fff4e5;
  --accent-border:#ffd199;
  --text-1:       #1a1b2e;
  --text-2:       #6b6d80;
  --text-3:       #a0a2b5;
  --success:      #16a34a;
  --success-bg:   #f0fdf4;
  --success-border:#bbf7d0;
  --error:        #dc2626;
  --error-bg:     #fff1f0;
  --error-border: #fecaca;
  --radius-sm:    8px;
  --radius-md:    14px;
  --radius-lg:    20px;
  --transition:   0.2s cubic-bezier(0.4, 0, 0.2, 1);
}

/* ───── Reset ───── */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

/* ───── Base ───── */
body {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  background: var(--bg);
  background-image:
    radial-gradient(ellipse 60% 50% at 80% 10%, rgba(255, 140, 0, 0.07) 0%, transparent 60%),
    radial-gradient(ellipse 50% 40% at 10% 90%, rgba(99, 102, 241, 0.05) 0%, transparent 60%);
  font-family: 'Inter', system-ui, sans-serif;
  color: var(--text-1);
  padding: 32px 16px 80px;
}

/* ───── Container ───── */
.container {
  width: 100%;
  max-width: 620px;
  display: flex;
  flex-direction: column;
  gap: 24px;
  animation: fadeUp 0.4s ease both;
}

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(18px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* ───── Header ───── */
.app-header {
  text-align: center;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 10px;
}

.icon-wrap {
  width: 52px;
  height: 52px;
  background: var(--accent-light);
  border: 1px solid var(--accent-border);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 10px;
  box-shadow: 0 2px 8px rgba(255, 140, 0, 0.15);
}

.icon-wrap svg { width: 100%; height: 100%; }

h1 {
  font-size: clamp(1.5rem, 5vw, 2rem);
  font-weight: 700;
  letter-spacing: -0.03em;
  color: var(--text-1);
  line-height: 1.2;
}

.accent-text {
  color: var(--accent);
}

.subtitle {
  font-size: 0.875rem;
  color: var(--text-2);
  font-weight: 400;
  max-width: 380px;
  line-height: 1.5;
}

/* ───── Card ───── */
.card {
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: var(--radius-lg);
  padding: 28px;
  box-shadow: var(--card-shadow);
  display: flex;
  flex-direction: column;
  gap: 20px;
}

/* ───── Input Grid ───── */
.input-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 14px;
}

.field-group {
  display: flex;
  flex-direction: column;
  gap: 5px;
}

label {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--text-2);
  text-transform: uppercase;
  letter-spacing: 0.055em;
}

.input-wrap {
  position: relative;
}

input[type="number"] {
  width: 100%;
  background: var(--input-bg);
  border: 1.5px solid var(--input-border);
  border-radius: var(--radius-sm);
  color: var(--text-1);
  font-family: inherit;
  font-size: 0.975rem;
  font-weight: 500;
  padding: 10px 36px 10px 12px;
  outline: none;
  transition: border-color var(--transition), box-shadow var(--transition), background var(--transition);
  -moz-appearance: textfield;
}

input[type="number"]::-webkit-inner-spin-button,
input[type="number"]::-webkit-outer-spin-button {
  -webkit-appearance: none;
}

input[type="number"]::placeholder {
  color: var(--text-3);
  font-weight: 400;
}

input[type="number"]:hover {
  border-color: #c8cad8;
  background: #ffffff;
}

input[type="number"]:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--input-focus);
  background: #ffffff;
}

input[type="number"].input-error {
  border-color: var(--error);
  box-shadow: 0 0 0 3px rgba(220, 38, 38, 0.15);
  background: var(--error-bg);
  animation: shake 0.35s ease;
}

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  20%       { transform: translateX(-5px); }
  40%       { transform: translateX(5px); }
  60%       { transform: translateX(-3px); }
  80%       { transform: translateX(3px); }
}

.unit-label {
  position: absolute;
  right: 11px;
  top: 50%;
  transform: translateY(-50%);
  font-size: 0.72rem;
  font-weight: 600;
  color: var(--text-3);
  pointer-events: none;
  user-select: none;
}

.field-hint {
  font-size: 0.68rem;
  color: var(--text-3);
  line-height: 1.3;
}

/* ───── Error message ───── */
.error-msg {
  font-size: 0.82rem;
  color: var(--error);
  background: var(--error-bg);
  border: 1px solid var(--error-border);
  border-radius: var(--radius-sm);
  padding: 9px 13px;
  display: none;
}

.error-msg.visible {
  display: block;
  animation: fadeIn 0.18s ease;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(-4px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* ───── Calculate Button ───── */
.btn-calculate {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  background: linear-gradient(135deg, var(--accent) 0%, var(--accent-2) 100%);
  color: #fff;
  font-family: inherit;
  font-size: 0.95rem;
  font-weight: 600;
  border: none;
  border-radius: var(--radius-sm);
  padding: 13px 24px;
  cursor: pointer;
  letter-spacing: 0.01em;
  box-shadow: 0 2px 12px rgba(255, 100, 0, 0.3), inset 0 1px 0 rgba(255,255,255,0.15);
  transition: transform var(--transition), box-shadow var(--transition), filter var(--transition);
  position: relative;
  overflow: hidden;
}

.btn-calculate::after {
  content: '';
  position: absolute;
  inset: 0;
  background: rgba(255, 255, 255, 0);
  transition: background var(--transition);
}

.btn-calculate:hover {
  transform: translateY(-1px);
  box-shadow: 0 4px 20px rgba(255, 100, 0, 0.4), inset 0 1px 0 rgba(255,255,255,0.15);
  filter: brightness(1.05);
}

.btn-calculate:active {
  transform: translateY(0);
  box-shadow: 0 1px 6px rgba(255, 100, 0, 0.25);
  filter: brightness(0.97);
}

.btn-icon {
  width: 16px;
  height: 16px;
  transition: transform var(--transition);
}

.btn-calculate:hover .btn-icon {
  transform: translateX(3px);
}

/* ───── Result Section ───── */
.result-section {
  border-top: 1px solid var(--card-border);
  padding-top: 20px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  text-align: center;
}

.result-label {
  font-size: 0.72rem;
  font-weight: 600;
  color: var(--text-2);
  text-transform: uppercase;
  letter-spacing: 0.07em;
}

.result-value {
  font-size: clamp(2rem, 8vw, 3rem);
  font-weight: 700;
  letter-spacing: -0.04em;
  color: var(--text-3);
  line-height: 1;
  min-height: 1.2em;
  transition: color var(--transition);
}

.result-value.has-result {
  color: var(--accent);
  animation: popIn 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

@keyframes popIn {
  from { transform: scale(0.85); opacity: 0; }
  to   { transform: scale(1);    opacity: 1; }
}

.result-sub {
  font-size: 0.76rem;
  color: var(--text-3);
  max-width: 300px;
  line-height: 1.5;
}

.result-sub strong {
  color: var(--text-2);
  font-weight: 500;
}

/* ───── Copy Button ───── */
.btn-copy {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--input-bg);
  border: 1.5px solid var(--input-border);
  border-radius: var(--radius-sm);
  color: var(--text-2);
  font-family: inherit;
  font-size: 0.82rem;
  font-weight: 500;
  padding: 8px 16px;
  cursor: pointer;
  transition: all var(--transition);
  margin-top: 4px;
}

.btn-copy svg {
  width: 14px;
  height: 14px;
  flex-shrink: 0;
}

.btn-copy:hover:not(:disabled) {
  background: #fff;
  border-color: #c8cad8;
  color: var(--text-1);
  transform: translateY(-1px);
  box-shadow: 0 2px 6px rgba(0,0,0,0.08);
}

.btn-copy:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.btn-copy.copied {
  background: var(--success-bg);
  border-color: var(--success-border);
  color: var(--success);
}

/* ───── Footer ───── */
.app-footer {
  text-align: center;
  font-size: 0.78rem;
  color: var(--text-3);
}

.app-footer strong {
  color: var(--text-2);
  font-weight: 500;
}

.app-footer a {
  color: var(--accent);
  text-decoration: none;
  font-weight: 500;
  transition: opacity var(--transition);
}

.app-footer a:hover { opacity: 0.7; }

/* ───── Responsive ───── */
@media (max-width: 500px) {
  .card { padding: 20px 16px; }

  .input-grid {
    grid-template-columns: 1fr;
    gap: 12px;
  }

  .field-hint { display: none; }
}