:root {
    --primary-color: #2563eb;
    --bg-color: #f3f4f6;
    --container-bg: #ffffff;
    --text-color: #1f2937;
    --border-color: #e5e7eb;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    color: var(--text-color);
    margin: 0;
    padding: 20px;
    display: flex;
    flex-direction: column;
    align-items: center;
    
    /* [배경 스타일 변경] */
    background-color: var(--bg-color); /* 기본 배경색 */
    /* 가로, 세로 격자 무늬 추가 */
    background-image: 
        linear-gradient(#e5e7eb 1px, transparent 1px), 
        linear-gradient(90deg, #e5e7eb 1px, transparent 1px);
    background-size: 20px 20px; /* 격자 크기 */
    min-height: 100vh; /* 화면이 짧아도 배경이 끊기지 않게 함 */
}

header h1 {
    color: var(--primary-color);
    margin-bottom: 20px;
}

nav {
    margin-bottom: 20px;
    display: flex;
    gap: 10px;
}

nav button {
    padding: 10px 20px;
    border: none;
    border-radius: 5px;
    background-color: #ddd;
    cursor: pointer;
    font-weight: bold;
    transition: background-color 0.3s;
}

nav button.active {
    background-color: var(--primary-color);
    color: white;
}

main {
    background-color: var(--container-bg);
    padding: 30px;
    border-radius: 10px;
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    width: 100%;
    max-width: 700px;
}

.calculator {
    display: none;
}

.calculator.active {
    display: block;
}

.input-group {
    margin-bottom: 15px;
    display: flex;
    align-items: center;
    gap: 10px;
}

.input-group label {
    width: 120px;
    font-weight: 500;
}

.input-group input, .input-group select {
    padding: 8px;
    border: 1px solid var(--border-color);
    border-radius: 4px;
}

.input-group input {
    flex: 1;
}

textarea {
    width: 100%;
    padding: 10px;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    margin-bottom: 10px;
    box-sizing: border-box;
    font-family: monospace;
}

button[id^="calculate"], button[id^="check"] {
    width: 100%;
    padding: 12px;
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: 4px;
    font-size: 1rem;
    cursor: pointer;
    margin-top: 10px;
}

button:hover {
    opacity: 0.9;
}

.result {
    margin-top: 20px;
    padding: 15px;
    background-color: #f8fafc;
    border-left: 4px solid var(--primary-color);
    white-space: pre-wrap;
    line-height: 1.6;
}

/* HED Layout Styling */
.hed-container {
    display: flex;
    gap: 20px;
    margin-bottom: 15px;
}

.hed-inputs {
    flex: 2;
}

.hed-reference {
    flex: 1;
    background-color: #f1f5f9;
    padding: 15px;
    border-radius: 8px;
    font-size: 0.85rem;
    height: fit-content;
}

.hed-reference h4 {
    margin-top: 0;
    margin-bottom: 10px;
    color: #4b5563;
    border-bottom: 1px solid #cbd5e1;
    padding-bottom: 5px;
}

.hed-reference ul {
    list-style: none;
    padding: 0;
    margin: 0;
}

.hed-reference li {
    margin-bottom: 4px;
    display: flex;
    justify-content: space-between;
}

.hed-group {
    background-color: #ffffff;
    border: 1px solid #e2e8f0;
    padding: 15px;
    border-radius: 6px;
    margin-bottom: 15px;
}

.hed-group h3 {
    margin-top: 0;
    font-size: 1rem;
    color: #4b5563;
    margin-bottom: 10px;
}

.warning-text {
    color: #b91c1c;
    font-size: 0.9rem;
    margin-bottom: 5px;
}

/* Responsive for mobile */
@media (max-width: 600px) {
    .hed-container {
        flex-direction: column;
    }
    .input-group {
        flex-direction: column;
        align-items: flex-start;
    }
    .input-group label {
        width: 100%;
        margin-bottom: 5px;
    }
    .input-group input, .input-group select {
        width: 100%;
    }
}

.ad-container {
    width: 100%;
    max-width: 700px;  /* 메인 콘텐츠 너비와 맞춤 */
    margin: 20px auto; /* 위아래 여백 20px, 좌우 중앙 정렬 */
    text-align: center;
    background-color: #fafafa;
    
    /* [수정된 부분] */
    height: 100px;      /* 높이를 100px로 딱 고정합니다 */
    /* 만약 광고 크기에 따라 조금 유연하게 하고 싶다면 height 대신 
       max-height: 120px; 등을 사용해도 됩니다. */
       
    overflow: hidden;   /* 광고가 100px보다 크면 넘치는 부분은 잘라냅니다 */
    
    /* [추가 팁] 광고를 박스 정중앙에 예쁘게 배치하려면 아래 3줄 추가 */
    display: flex;
    align-items: center;
    justify-content: center;
}