.keisan-app {
  --keisan-bg: #f7fbff;
  --keisan-panel: #ffffff;
  --keisan-text: #18202a;
  --keisan-muted: #526173;
  --keisan-line: #d9e4ef;
  --keisan-main: #1c7ed6;
  --keisan-main-dark: #145fa3;
  --keisan-choice: #f3f8fc;
  --keisan-choice-hover: #e5f2ff;
  --keisan-correct: #197c4d;
  --keisan-wrong: #b42318;
  box-sizing: border-box;
  min-height: 100vh;
  padding: 24px 16px;
  color: var(--keisan-text);
  background: var(--keisan-bg);
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Hiragino Sans", "Yu Gothic", sans-serif;
}

.keisan-app *,
.keisan-app *::before,
.keisan-app *::after {
  box-sizing: inherit;
}

.keisan-app__panel {
  width: min(100%, 840px);
  margin: 0 auto;
  padding: 24px;
  border: 1px solid var(--keisan-line);
  border-radius: 8px;
  background: var(--keisan-panel);
}

.keisan-app__header {
  display: flex;
  gap: 16px;
  align-items: flex-start;
  justify-content: space-between;
  margin-bottom: 18px;
}

.keisan-app__title {
  margin: 0;
  font-size: 2rem;
  line-height: 1.2;
}

.keisan-app__status {
  display: grid;
  gap: 4px;
  min-width: 124px;
  text-align: right;
}

.keisan-app__counter,
.keisan-app__score {
  margin: 0;
  color: var(--keisan-muted);
  font-size: 1.05rem;
  font-weight: 700;
}

.keisan-app__level-label {
  display: block;
  margin-bottom: 8px;
  color: var(--keisan-muted);
  font-size: 1rem;
  font-weight: 700;
}

.keisan-app__level-select {
  width: 100%;
  min-height: 52px;
  margin-bottom: 22px;
  padding: 10px 12px;
  border: 2px solid var(--keisan-line);
  border-radius: 8px;
  background: #ffffff;
  color: var(--keisan-text);
  font-size: 1.1rem;
}

.keisan-app__message {
  min-height: 48px;
  margin-bottom: 10px;
  font-size: 1.5rem;
  font-weight: 800;
  line-height: 1.4;
}

.keisan-app__message--correct {
  color: var(--keisan-correct);
}

.keisan-app__message--wrong {
  color: var(--keisan-wrong);
}

.keisan-app__message--done {
  color: var(--keisan-main-dark);
}

.keisan-app__question {
  min-height: 76px;
  margin: 0 0 22px;
  font-size: 2.7rem;
  line-height: 1.25;
  overflow-wrap: anywhere;
}

.keisan-app__choices {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
}

.keisan-app__choice {
  min-height: 112px;
  padding: 12px;
  border: 2px solid var(--keisan-line);
  border-radius: 8px;
  background: var(--keisan-choice);
  color: var(--keisan-text);
  font-size: 3.5rem;
  font-weight: 800;
  line-height: 1;
  cursor: pointer;
  touch-action: manipulation;
}

.keisan-app__choice:hover,
.keisan-app__choice:focus-visible {
  border-color: var(--keisan-main);
  background: var(--keisan-choice-hover);
  outline: none;
}

.keisan-app__choice:disabled {
  cursor: default;
  opacity: 0.75;
}

.keisan-app__choice--division {
  font-size: 2.15rem;
  line-height: 1.08;
}

.keisan-app__next-button,
.keisan-app__restart-button {
  display: block;
  width: min(100%, 360px);
  min-height: 78px;
  margin: 20px auto 0;
  border: 0;
  border-radius: 8px;
  background: var(--keisan-main);
  color: #ffffff;
  font-size: 1.8rem;
  font-weight: 800;
  cursor: pointer;
  touch-action: manipulation;
}

.keisan-app__next-button:hover,
.keisan-app__next-button:focus-visible,
.keisan-app__restart-button:hover,
.keisan-app__restart-button:focus-visible {
  background: var(--keisan-main-dark);
  outline: none;
}

.keisan-app__next-button[hidden],
.keisan-app__restart-button[hidden] {
  display: none;
}

@media (max-width: 640px) {
  .keisan-app {
    padding: 12px;
  }

  .keisan-app__panel {
    padding: 18px 14px;
  }

  .keisan-app__header {
    display: grid;
    gap: 8px;
  }

  .keisan-app__status {
    min-width: 0;
    text-align: left;
  }

  .keisan-app__title {
    font-size: 1.7rem;
  }

  .keisan-app__question {
    min-height: 62px;
    font-size: 2.15rem;
  }

  .keisan-app__choices {
    gap: 10px;
  }

  .keisan-app__choice {
    min-height: 96px;
    font-size: 2.8rem;
  }

  .keisan-app__choice--division {
    font-size: 1.75rem;
  }

  .keisan-app__message {
    min-height: 42px;
    font-size: 1.25rem;
  }

  .keisan-app__next-button,
  .keisan-app__restart-button {
    min-height: 70px;
    font-size: 1.5rem;
  }
}

@media (max-width: 360px) {
  .keisan-app__choices {
    grid-template-columns: 1fr;
  }
}