:root {
    --bg-color: #f0f2f5;
    --container-bg: #ffffff;
    --text-color: #333;
    --primary-color: #4a90e2;
    --border-color: #333;
    --cell-border: #ccc;
    --selected-bg: #e2eefd;
    --related-bg: #f5f7f9;
    --fixed-text: #000;
    --user-text: #4a90e2;
    --error-bg: #fee2e2;
    --error-text: #ef4444;
    --memo-text: #666;
    --numpad-btn-bg: #ffffff;
    --numpad-erase-bg: #f8f9fa;
}

[data-theme="dark"] {
    --bg-color: #121212;
    --container-bg: #1e1e1e;
    --text-color: #e0e0e0;
    --primary-color: #6ba4e8;
    --border-color: #ffffff;
    --cell-border: #444444;
    --selected-bg: #1a365d;
    --related-bg: #2d3748;
    --fixed-text: #ffffff;
    --user-text: #6ba4e8;
    --error-bg: #4a1d1d;
    --error-text: #fca5a5;
    --memo-text: #aaa;
    --numpad-btn-bg: #2d2d2d;
    --numpad-erase-bg: #3a3a3a;
}

body {
    font-family: 'Pretendard', -apple-system, BlinkMacSystemFont, system-ui, Roboto, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
}

.container {
    background-color: var(--container-bg);
    padding: 2rem;
    border-radius: 12px;
    box-shadow: 0 10px 25px rgba(0,0,0,0.1);
    width: 100%;
    max-width: 500px;
    text-align: center;
}

h1 {
    margin-bottom: 1.5rem;
    color: var(--primary-color);
}

.controls {
    margin-bottom: 1.5rem;
}

.info {
    display: flex;
    justify-content: space-between;
    margin-bottom: 1rem;
    font-weight: 600;
    font-size: 1.1rem;
}

.actions {
    display: flex;
    gap: 10px;
    justify-content: center;
}

select, button {
    padding: 8px 16px;
    border-radius: 6px;
    border: 1px solid var(--cell-border);
    background-color: var(--container-bg);
    color: var(--text-color);
    font-size: 1rem;
    cursor: pointer;
}

#new-game-btn {
    background-color: var(--primary-color);
    color: white;
    border: none;
    transition: background-color 0.2s;
}

#new-game-btn:hover {
    background-color: #357abd;
}

.ux-tip {
    text-align: center; 
    margin: 0.5rem 0 1rem 0; 
    font-size: 0.85rem; 
    color: var(--memo-text); 
    line-height: 1.4;
}

.sudoku-grid {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    grid-template-rows: repeat(9, 1fr); /* ◀ 모바일 사파리 등에서 일관된 행 높이를 유지하도록 명시 */
    border: 2px solid var(--border-color);
    margin: 0 auto 1.5rem;
    width: 100%;
    aspect-ratio: 1 / 1;
}

.cell {
    border: 1px solid var(--cell-border);
    position: relative;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.5rem;
    cursor: pointer;
    user-select: none;
    transition: background-color 0.1s;
    box-sizing: border-box; /* ◀ 테두리가 너비/높이에 포함되도록 고정 */
    aspect-ratio: 1 / 1;    /* ◀ 셀 단위에서도 정사각형 비율 고정 */
    overflow: hidden;       /* ◀ 텍스트나 메모 그리드가 넘쳐서 늘어나는 현상 방지 */
}

.memo-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(3, 1fr);
    width: 100%;
    height: 100%;
    padding: 2px;
    box-sizing: border-box;
}

.memo-item {
    font-size: 0.6rem;
    color: var(--memo-text);
    display: flex;
    justify-content: center;
    align-items: center;
    line-height: 1;
}

/* 3x3 Block Borders */
.cell:nth-child(3n) { border-right: 1px solid var(--cell-border); }
.cell:nth-child(3n):not(:nth-child(9n)) { border-right: 2px solid var(--border-color); }
.cell:nth-child(n+19):nth-child(-n+27),
.cell:nth-child(n+46):nth-child(-n+54) {
    border-bottom: 2px solid var(--border-color);
}

.cell.fixed { font-weight: bold; color: var(--fixed-text); }
.cell.user-input { color: var(--user-text); }
.cell.selected { background-color: var(--selected-bg); }
.cell.related { background-color: var(--related-bg); }
.cell.error { background-color: var(--error-bg); color: var(--error-text); }
.cell.same-number { background-color: rgba(255, 235, 59, 0.25); }

/* 💡 넘버패드 6열 레이아웃 배치 수정 */
.number-pad {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 8px;
    margin-top: 1rem;
}

.numpad-btn {
    padding: 12px;
    border: 1px solid var(--cell-border);
    background-color: var(--numpad-btn-bg);
    color: var(--text-color);
    border-radius: 8px;
    font-size: 1.2rem;
    font-weight: 600;
    transition: all 0.2s;
    cursor: pointer;
}

.numpad-btn:hover {
    background-color: var(--selected-bg);
    border-color: var(--primary-color);
}

/* 지우기 버튼과 되돌리기 버튼 하단 정렬 스타일 */
.numpad-btn[data-number="erase"] {
    grid-column: span 2;
    background-color: var(--numpad-erase-bg);
}

#undo-btn {
    grid-column: span 2;
    background-color: var(--numpad-erase-bg);
}

.message {
    margin-top: 1rem;
    font-weight: 600;
    min-height: 1.5rem;
}

/* --- Custom Restore Modal Styles --- */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.6);
    backdrop-filter: blur(4px);
    display: none; /* Toggled to flex by JS */
    justify-content: center;
    align-items: center;
    z-index: 1000;
}

.modal-overlay .modal-content {
    background-color: var(--container-bg);
    color: var(--text-color);
    padding: 2.2rem 2rem;
    border-radius: 16px;
    box-shadow: 0 15px 35px rgba(0, 0, 0, 0.3);
    max-width: 380px;
    width: 88%;
    text-align: center;
    border: 1px solid var(--cell-border);
    animation: modalFadeIn 0.3s cubic-bezier(0.25, 0.8, 0.25, 1);
}

.modal-overlay h2 {
    color: var(--primary-color);
    margin-top: 0;
    margin-bottom: 0.8rem;
    font-size: 1.5rem;
}

.modal-overlay p {
    font-size: 1rem;
    line-height: 1.6;
    margin-bottom: 1.8rem;
    color: var(--text-color);
}

.modal-overlay .modal-buttons {
    display: flex;
    gap: 12px;
    justify-content: center;
}

.modal-overlay button {
    padding: 12px 24px;
    font-weight: bold;
    border-radius: 8px;
    cursor: pointer;
    font-size: 0.95rem;
    border: none;
    transition: all 0.2s;
}

#restore-yes-btn {
    background-color: var(--primary-color);
    color: white;
}

#restore-yes-btn:hover {
    filter: brightness(1.1);
    transform: translateY(-1px);
}

#restore-no-btn.cancel-btn {
    background-color: #e2e8f0;
    color: #475569;
}

[data-theme="dark"] #restore-no-btn.cancel-btn {
    background-color: #334155;
    color: #cbd5e1;
}

#restore-no-btn.cancel-btn:hover {
    filter: brightness(0.9);
    transform: translateY(-1px);
}

@keyframes modalFadeIn {
    from { opacity: 0; transform: scale(0.92) translateY(-15px); }
    to { opacity: 1; transform: scale(1) translateY(0); }
}

@media (max-width: 400px) {
    .container { padding: 1rem; }
    .cell { font-size: 1.2rem; }
}

/* --- Custom Win Modal Styles --- */
.modal-overlay .win-modal-content {
    max-width: 420px;
    padding: 2.5rem 2rem;
    border: 2px solid #10b981;
}

.modal-overlay .fanfare-img {
    width: 120px;
    height: 120px;
    object-fit: contain;
    margin-bottom: 1rem;
    animation: bounce 1.5s infinite alternate;
}

.modal-overlay .win-message {
    font-size: 1.2rem;
    font-weight: bold;
    color: #10b981;
    margin-bottom: 0.5rem;
}

#win-time-display {
    font-size: 1.1rem;
    color: var(--text-color);
    margin-bottom: 1.5rem;
    font-weight: 600;
}

#win-new-game-btn {
    background-color: #10b981;
    color: white;
}

#win-new-game-btn:hover {
    background-color: #059669;
    transform: translateY(-1px);
}

#win-close-btn.cancel-btn {
    background-color: #e2e8f0;
    color: #475569;
}

[data-theme="dark"] #win-close-btn.cancel-btn {
    background-color: #334155;
    color: #cbd5e1;
}

#win-close-btn.cancel-btn:hover {
    filter: brightness(0.9);
    transform: translateY(-1px);
}

@keyframes bounce {
    from { transform: translateY(0); }
    to { transform: translateY(-10px); }
}

/* --- Completed Number Pad Button Styles (Option B) --- */
.numpad-btn.completed-disabled {
    opacity: 0.25;
    pointer-events: none;
    cursor: default;
    position: relative;
    border-color: var(--cell-border);
    background-color: var(--numpad-erase-bg);
}

.numpad-btn.completed-disabled::after {
    content: "✓";
    position: absolute;
    top: 2px;
    right: 5px;
    font-size: 0.75rem;
    color: #10b981;
    font-weight: bold;
}