:root {
  --accent: #7865a8;
  --accent-dark: #514473;
  --wash: #cec1e6;
  --wrong: #b84f43;
}

.addition-stage {
  width: min(100%, 680px);
}

.addition-card {
  position: relative;
  overflow: hidden;
  min-height: min(35vh, 300px);
  min-height: min(35dvh, 300px);
  padding: 24px 14px;
  border: 1px solid color-mix(in srgb, var(--accent) 24%, transparent);
  border-radius: 34px;
  background:
    linear-gradient(145deg, rgba(255, 255, 255, 0.82), rgba(255, 255, 255, 0.32)),
    var(--wash);
  box-shadow: var(--shadow);
}

.addition-card::after {
  position: absolute;
  right: -42px;
  bottom: -52px;
  width: 126px;
  height: 126px;
  border: 2px solid color-mix(in srgb, var(--accent) 18%, transparent);
  border-radius: 50%;
  content: "";
}

.addition-row {
  position: relative;
  z-index: 1;
  display: grid;
  min-height: inherit;
  grid-template-columns: minmax(0, 1fr) 38px minmax(0, 1fr);
  align-items: center;
  gap: 5px;
}

.addend {
  display: grid;
  min-width: 0;
  min-height: 190px;
  grid-template-rows: 1fr auto;
  align-items: center;
  justify-items: center;
  gap: 12px;
  padding: 14px 8px 8px;
  border-radius: 24px;
  background: rgba(255, 255, 255, 0.46);
}

.addend-grid {
  display: flex;
  width: 100%;
  flex-wrap: wrap;
  align-content: center;
  align-items: center;
  justify-content: center;
  gap: clamp(6px, 2vw, 11px);
}

.addend-object {
  display: grid;
  flex: 0 0 clamp(42px, 11vw, 62px);
  aspect-ratio: 1;
  place-items: center;
  font-size: clamp(2.25rem, 10vw, 3.6rem);
  line-height: 1;
  filter: drop-shadow(0 4px 5px rgba(32, 48, 41, 0.11));
}

.addition-card.is-changing .addend-object {
  animation: object-pop 290ms cubic-bezier(0.2, 0.85, 0.35, 1.2) both;
  animation-delay: calc(var(--object-index) * 34ms);
}

.number-badge {
  display: grid;
  min-width: 38px;
  height: 34px;
  padding-inline: 9px;
  place-items: center;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.76);
  color: var(--accent-dark);
  font-family: "Nunito", sans-serif;
  font-size: 1.2rem;
  font-weight: 900;
}

.plus-sign {
  display: grid;
  width: 38px;
  height: 38px;
  place-items: center;
  border-radius: 50%;
  background: var(--surface);
  box-shadow: 0 6px 18px rgba(32, 48, 41, 0.09);
  color: var(--accent-dark);
  font-family: "Nunito", sans-serif;
  font-size: 1.65rem;
  font-weight: 900;
}

.feedback {
  min-height: 25px;
  margin: 14px 0 10px;
  color: var(--muted);
  font-size: 0.88rem;
  font-weight: 800;
}

.feedback.is-correct { color: var(--accent-dark); }
.feedback.is-wrong { color: var(--wrong); }

.answer-options {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
}

.answer-button {
  min-height: 68px;
  border: 2px solid color-mix(in srgb, var(--accent) 20%, var(--line));
  border-radius: 22px;
  background: var(--surface);
  box-shadow: 0 8px 20px rgba(32, 48, 41, 0.07);
  color: var(--ink);
  cursor: pointer;
  font-family: "Nunito", sans-serif;
  font-size: clamp(1.8rem, 8vw, 2.45rem);
  font-weight: 900;
  -webkit-tap-highlight-color: transparent;
  touch-action: manipulation;
  transition: transform 150ms ease, border-color 150ms ease, background 150ms ease;
}

.answer-button:hover { transform: translateY(-2px); border-color: var(--accent); }
.answer-button:active { transform: scale(0.97); }
.answer-button:disabled { cursor: default; }

.answer-button.is-correct {
  border-color: var(--accent);
  background: color-mix(in srgb, var(--wash) 55%, white);
  color: var(--accent-dark);
}

.answer-button.is-wrong {
  border-color: var(--wrong);
  animation: gentle-shake 280ms ease;
}

@keyframes object-pop {
  0% { opacity: 0; transform: scale(0.58) translateY(7px); }
  100% { opacity: 1; transform: scale(1) translateY(0); }
}

@keyframes gentle-shake {
  0%, 100% { transform: translateX(0); }
  35% { transform: translateX(-5px); }
  70% { transform: translateX(5px); }
}

@media (min-width: 700px) {
  .addition-card {
    min-height: min(40vh, 350px);
    min-height: min(40dvh, 350px);
    padding: 28px;
    border-radius: 42px;
  }

  .addition-row {
    grid-template-columns: minmax(0, 1fr) 54px minmax(0, 1fr);
    gap: 12px;
  }

  .addend {
    min-height: 235px;
  }

  .plus-sign {
    width: 48px;
    height: 48px;
    font-size: 1.9rem;
  }

  .answer-options { gap: 14px; }
  .answer-button { min-height: 80px; border-radius: 25px; }
}

@media (max-height: 650px) {
  .addition-card { min-height: 210px; padding-block: 14px; }
  .addend { min-height: 170px; }
  .feedback { margin-block: 8px 6px; }
  .answer-button { min-height: 58px; }
}