.open-sentence-prompt {
    font-size: 1.1rem;
    font-weight: 600;
    color: #444;
    text-align: center;
    margin: 0.5rem 0 0.6rem;
}

.open-sentence-substitution {
    font-size: 1.05rem;
    font-weight: 600;
    color: #1f3a5f;
    text-align: center;
    margin: 0 0 0.5rem;
}

.open-sentence-expression {
    display: flex;
    align-items: center;
    justify-content: center;
    min-height: 5rem;
    margin: 0 auto 1.25rem;
    padding: 0.75rem 1.5rem;
    font-size: 2.2rem;
    font-weight: 700;
    letter-spacing: 0.05em;
    color: #1f3a5f;
    background: #f4f8ff;
    border: 2px solid #bcd4f6;
    border-radius: 16px;
}

.open-sentence-options {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 1rem;
    margin-bottom: 1rem;
}

.open-sentence-option {
    min-width: 7rem;
    padding: 0.9rem 1.4rem;
    font-size: 1.4rem;
    font-weight: 700;
    color: #1f3a5f;
    background: #ffffff;
    border: 2px solid #bcd4f6;
    border-radius: 14px;
    cursor: pointer;
    transition: transform 0.1s ease, box-shadow 0.1s ease;
}

.open-sentence-option:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 10px rgba(31, 58, 95, 0.15);
}

.open-sentence-true {
    border-color: #9ed4a3;
}

.open-sentence-false {
    border-color: #f0b4b4;
}

.open-sentence-hint {
    text-align: left;
}

.open-sentence-hint p {
    margin: 0.35rem 0;
}