/* 전체 기본 스타일 */
* {
    box-sizing: border-box;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", system-ui, sans-serif;
}

body {
    margin: 0;
    padding: 0;
    background: #f4f6fb;
    color: #222;
}

/* 앱 컨테이너 */
.app-container {
    max-width: 480px;
    margin: 0 auto;
    padding: 16px 16px 40px;
}

/* 제목 */
h1 {
    font-size: 1.6rem;
    text-align: center;
    margin: 18px 0 8px;
}

.subtitle {
    text-align: center;
    font-size: 0.9rem;
    color: #666;
    margin-bottom: 16px;
}

/* 입력 카드 */
.card {
    background: #ffffff;
    border-radius: 12px;
    padding: 16px 14px 18px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.06);
}

/* 입력 그룹 */
.input-group {
    margin-bottom: 12px;
}

.input-group label {
    display: block;
    font-size: 0.9rem;
    margin-bottom: 4px;
    color: #333;
}

.input-group input {
    width: 100%;
    padding: 8px 10px;
    font-size: 0.95rem;
    border-radius: 8px;
    border: 1px solid #d0d4e0;
    outline: none;
    transition: border-color 0.15s ease, box-shadow 0.15s ease;
}

.input-group input:focus {
    border-color: #4a6cf7;
    box-shadow: 0 0 0 2px rgba(74, 108, 247, 0.18);
}

/* 버튼 */
button#calcButton {
    width: 100%;
    padding: 10px 12px;
    font-size: 1rem;
    margin-top: 6px;
    border-radius: 10px;
    border: none;
    background: #4a6cf7;
    color: #ffffff;
    cursor: pointer;
    font-weight: 600;
    letter-spacing: 0.03em;
    transition: background 0.15s ease, transform 0.05s ease;
}

button#calcButton:hover {
    background: #3b59d1;
}

button#calcButton:active {
    transform: scale(0.99);
}

/* 결과 박스 */
.result-box {
    margin-top: 14px;
    padding: 10px 10px;
    border-radius: 10px;
    background: #f5f7ff;
    border: 1px solid #d6ddff;
    font-size: 0.95rem;
    line-height: 1.4;
}

/* 에러 박스 */
.error-box {
    margin-top: 8px;
    padding: 8px 10px;
    border-radius: 10px;
    background: #ffecec;
    border: 1px solid #ffbcbc;
    color: #b00020;
    font-size: 0.85rem;
}

/* 수식 카드 */
.formula-card {
    margin-top: 18px;
    padding: 12px 14px 14px;
    background: #ffffff;
    border-radius: 12px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.04);
}

.formula-card h2 {
    font-size: 1rem;
    margin: 0 0 8px;
}

.formula {
    font-family: "SF Mono", "Roboto Mono", Consolas, monospace;
    font-size: 0.9rem;
    background: #f4f6ff;
    padding: 6px 8px;
    border-radius: 6px;
    margin-bottom: 8px;
}

.formula-desc {
    margin: 0;
    padding-left: 18px;
    font-size: 0.85rem;
    color: #555;
}

.formula-desc li {
    margin-bottom: 3px;
}

/* 모바일에서 보기 좋게 */
@media (max-width: 480px) {
    h1 {
        font-size: 1.45rem;
    }

    .card, .formula-card {
        padding: 14px 12px 16px;
    }
}