:root {
  --ink: #0f2a2e;
  --ink-soft: #3d5a5f;
  --paper: #f4fbf9;
  --accent: #0d8a78;
  --accent-deep: #066657;
  --glow: #7ed9c8;
  --sky: #b8e4f0;
  --font-display: "Fraunces", Georgia, serif;
  --font-body: "Outfit", system-ui, sans-serif;
  --ease: cubic-bezier(0.22, 1, 0.36, 1);
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  height: 100%;
}

body {
  margin: 0;
  min-height: 100%;
  font-family: var(--font-body);
  color: var(--ink);
  background: var(--paper);
  line-height: 1.45;
  -webkit-font-smoothing: antialiased;
}

.bg {
  position: fixed;
  inset: 0;
  z-index: -1;
  background:
    radial-gradient(ellipse 80% 60% at 10% 0%, var(--glow) 0%, transparent 55%),
    radial-gradient(ellipse 70% 50% at 90% 10%, var(--sky) 0%, transparent 50%),
    linear-gradient(165deg, #e8f7f3 0%, #d6eef8 45%, #f0f7f4 100%);
  animation: bgDrift 18s ease-in-out infinite alternate;
}

@keyframes bgDrift {
  from {
    filter: hue-rotate(0deg);
    transform: scale(1);
  }
  to {
    filter: hue-rotate(12deg);
    transform: scale(1.03);
  }
}

.shell {
  width: min(28rem, calc(100% - 2rem));
  margin: 0 auto;
  padding: clamp(2.5rem, 8vh, 4.5rem) 0 3rem;
  animation: riseIn 0.7s var(--ease) both;
}

@keyframes riseIn {
  from {
    opacity: 0;
    transform: translateY(1.25rem);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.brand {
  margin-bottom: 1.25rem;
}

.brand__name {
  margin: 0;
  font-family: var(--font-display);
  font-size: clamp(2.6rem, 9vw, 3.4rem);
  font-weight: 700;
  letter-spacing: -0.03em;
  line-height: 1.05;
  color: var(--accent-deep);
}

.brand__tag {
  margin: 0.35rem 0 0;
  font-size: 1.05rem;
  color: var(--ink-soft);
  font-weight: 400;
}

.month {
  margin: 0 0 1.75rem;
  font-size: 0.95rem;
  font-weight: 500;
  color: var(--ink-soft);
  letter-spacing: 0.01em;
}

.modes {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.4rem;
  margin-bottom: 1.75rem;
  padding: 0.35rem;
  background: color-mix(in srgb, white 55%, transparent);
  border-radius: 999px;
  backdrop-filter: blur(8px);
}

.modes__btn {
  appearance: none;
  border: 0;
  border-radius: 999px;
  padding: 0.7rem 0.85rem;
  font: inherit;
  font-size: 0.92rem;
  font-weight: 500;
  color: var(--ink-soft);
  background: transparent;
  cursor: pointer;
  transition:
    background 0.35s var(--ease),
    color 0.35s var(--ease),
    transform 0.25s var(--ease);
}

.modes__btn:hover {
  color: var(--ink);
}

.modes__btn.is-active {
  background: var(--ink);
  color: white;
  box-shadow: 0 8px 24px color-mix(in srgb, var(--ink) 18%, transparent);
}

.modes__btn:active {
  transform: scale(0.98);
}

.form {
  display: flex;
  flex-direction: column;
  gap: 1.15rem;
  margin-bottom: 2rem;
}

.field {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
  transition:
    opacity 0.35s var(--ease),
    transform 0.35s var(--ease);
}

.field.is-hidden {
  display: none;
}

.field__label {
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--ink-soft);
  letter-spacing: 0.02em;
}

.field__optional {
  font-weight: 400;
  opacity: 0.65;
}

.field__input {
  display: flex;
  align-items: center;
  gap: 0.15rem;
}

.field__prefix {
  font-size: 1.35rem;
  font-weight: 500;
  color: var(--accent);
  padding-left: 0.15rem;
}

input[type="number"] {
  width: 100%;
  appearance: textfield;
  border: 0;
  border-bottom: 2px solid color-mix(in srgb, var(--ink) 18%, transparent);
  border-radius: 0;
  padding: 0.55rem 0.2rem;
  font: inherit;
  font-size: 1.45rem;
  font-weight: 500;
  color: var(--ink);
  background: transparent;
  outline: none;
  transition: border-color 0.25s var(--ease);
}

input[type="number"]::-webkit-outer-spin-button,
input[type="number"]::-webkit-inner-spin-button {
  appearance: none;
  margin: 0;
}

input[type="number"]:focus {
  border-color: var(--accent);
}

.result {
  min-height: 7.5rem;
  animation: riseIn 0.85s var(--ease) 0.12s both;
}

.result__label {
  margin: 0 0 0.25rem;
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--ink-soft);
  text-transform: lowercase;
  letter-spacing: 0.04em;
}

.result__value {
  margin: 0;
  font-family: var(--font-display);
  font-size: clamp(2.4rem, 10vw, 3.2rem);
  font-weight: 700;
  letter-spacing: -0.03em;
  line-height: 1.1;
  color: var(--accent-deep);
}

.result__value.is-pulse {
  animation: pulseValue 0.45s var(--ease);
}

@keyframes pulseValue {
  0% {
    transform: scale(1);
    opacity: 0.65;
  }
  45% {
    transform: scale(1.03);
    opacity: 1;
  }
  100% {
    transform: scale(1);
    opacity: 1;
  }
}

.result__hint {
  margin: 0.65rem 0 0;
  font-size: 1rem;
  font-weight: 500;
  color: var(--ink);
  opacity: 0.85;
}

.result__hint.is-hidden {
  display: none;
}

@media (min-width: 640px) {
  .shell {
    width: min(32rem, calc(100% - 3rem));
  }
}