/* CSS Variables for theming */
:root {
    --bg-color: #f0f2f5;
    --text-color: #333;
    --container-bg: white;
    --border-color: #ccc;
    --strong-border-color: #333;
    --given-cell-bg: #e9ecef;
    --primary-btn-bg: #007bff;
    --primary-btn-hover: #0056b3;
    --secondary-btn-bg: #28a745;
    --secondary-btn-hover: #218838;
    --error-bg: #ffdddd;
    --error-text: #d8000c;
    --footer-text-color: #6c757d;
    --selected-cell-bg: #d0e7ff;
    --rc-highlight-bg: rgba(0, 0, 0, 0.07);
    --grid-highlight-bg: rgba(0, 123, 255, 0.08);
}

.dark-mode {
    --bg-color: #121212;
    --text-color: #e0e0e0;
    --container-bg: #1e1e1e;
    --border-color: #444;
    --strong-border-color: #888;
    --given-cell-bg: #2c2c2c;
    --primary-btn-bg: #0056b3;
    --primary-btn-hover: #003d82;
    --secondary-btn-bg: #218838;
    --secondary-btn-hover: #1e7e34;
    --error-bg: #5c1f1f;
    --error-text: #ff9999;
    --footer-text-color: #888;
    --selected-cell-bg: #003d82;
    --rc-highlight-bg: rgba(255, 255, 255, 0.07);
    --grid-highlight-bg: rgba(0, 123, 255, 0.1);
}

body {
    font-family: sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
    background-color: var(--bg-color);
    color: var(--text-color);
    transition: background-color 0.3s, color 0.3s;
    padding: 10px;
    padding-bottom: 80px;
    margin: 0;
    box-sizing: border-box;
}

h1 {
    font-size: clamp(2rem, 8vw, 2.5rem);
    margin-bottom: 10px;
    text-align: center;
}

.controls {
    margin: 10px 0;
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    align-items: center;
    justify-content: center;
}
select, button, .guide-btn {
    padding: 8px 12px;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    font-size: 16px;
    background-color: var(--container-bg);
    color: var(--text-color);
    text-decoration: none; /* For <a> tags styled as buttons */
}
button, .guide-btn {
    background-color: var(--primary-btn-bg);
    color: white;
    cursor: pointer;
}
button:hover, .guide-btn:hover {
    background-color: var(--primary-btn-hover);
}
#theme-toggle-btn {
    background-color: #6c757d;
}
#theme-toggle-btn:hover {
    background-color: #5a6268;
}
.guide-btn {
    background-color: var(--secondary-btn-bg);
}
.guide-btn:hover {
    background-color: var(--secondary-btn-hover);
}


/* Pre-game State: Hide game-specific elements */
.timer-container,
#pause-btn,
#solve-btn,
#number-pad {
    display: none;
}

/* Active Game State: Show elements */
body.game-active .timer-container,
body.game-active #pause-btn,
body.game-active #solve-btn,
body.game-active #number-pad {
    display: flex;
}

.timer-container {
    font-size: 1rem;
    background-color: var(--container-bg);
    color: var(--text-color);
    padding: 8px 15px;
    border-radius: 4px;
    border: 1px solid var(--border-color);
}
.timer-container span + span {
    margin-left: 20px;
}

/* Board and Cell styles */
#board-container {
    position: relative;
    margin-top: 20px;
}
#sudoku-board {
    display: grid;
    width: 90vw;
    height: 90vw;
    max-width: 450px;
    max-height: 450px;
    grid-template-columns: repeat(9, 1fr);
    grid-template-rows: repeat(9, 1fr);
    border: 3px solid var(--strong-border-color);
}
.cell {
    background-color: var(--container-bg);
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: clamp(16px, 4vw, 24px);
    box-sizing: border-box;
    color: var(--text-color);
    transition: background-color 0.2s; /* Smooth transition for selection */
}
.cell.highlight-rc {
    background-color: var(--rc-highlight-bg);
}
.cell.highlight-grid {
    background-color: var(--grid-highlight-bg);
}
.cell.selected {
    background-color: var(--selected-cell-bg);
}
.cell input {
    width: 100%; height: 100%; border: none; text-align: center;
    font-size: inherit;
    padding: 0;
    background-color: transparent; color: var(--text-color);
    caret-color: var(--text-color);
}
.cell.given { background-color: var(--given-cell-bg); font-weight: bold; }
.cell.pregame-cell { color: var(--text-color); opacity: 0.2; font-weight: bold; }
.cell { border-top: 1px solid var(--border-color); border-left: 1px solid var(--border-color); }
.cell.border-bottom { border-bottom: 3px solid var(--strong-border-color); }
.cell.border-right { border-right: 3px solid var(--strong-border-color); }

/* Number Pad Styles */
#number-pad {
    flex-wrap: wrap;
    justify-content: center;
    gap: 5px;
    margin-top: 20px;
    max-width: 90vw;
}
.num-btn {
    width: 45px;
    height: 45px;
    font-size: 1.5rem;
    display: flex;
    justify-content: center;
    align-items: center;
}
#erase-btn {
    background-color: #dc3545; /* Red for erase button */
}
#erase-btn:hover {
    background-color: #c82333;
}

/* Modal Styles */
.modal-overlay {
    position: fixed; top: 0; left: 0; width: 100%; height: 100%; background-color: rgba(0, 0, 0, 0.7);
    display: flex; justify-content: center; align-items: center; z-index: 1000;
}
.modal-content {
    background-color: var(--container-bg); color: var(--text-color); padding: 30px; border-radius: 10px;
    text-align: center; box-shadow: 0 5px 15px rgba(0,0,0,0.3); max-width: 90%; width: 500px;
}
.modal-content h2 { margin-top: 0; }
.modal-content p { margin-bottom: 20px; }
#congrats-modal h2 { color: #007bff; }
.balloons { font-size: 48px; animation: float 3s ease-in-out infinite; }
@keyframes float { 0%, 100% { transform: translateY(0); } 50% { transform: translateY(-20px); } }

#error-modal h2 { color: var(--error-text); }
#error-modal button { background-color: var(--error-text); }
#error-modal button:hover { background-color: #a00009; }
#error-list { list-style-type: none; padding: 0; margin-bottom: 20px; }
.cell input.error { background-color: var(--error-bg); color: var(--text-color); font-weight: bold; }

/* Page Content Container */
.page-container {
    background-color: var(--container-bg); padding: 20px 20px; border-radius: 8px; margin: 20px;
    max-width: 800px; text-align: left; border: 1px solid var(--border-color);
}
.page-container h2 { margin-top: 0; }
.page-container a.home-link {
    display: inline-block; margin-bottom: 30px; text-decoration: none;
    font-weight: bold; color: var(--primary-btn-bg);
}
.page-container a.home-link:hover { text-decoration: underline; }

/* --- NEW STYLES FOR GUIDE PAGE --- */
.guide-image {
    max-width: 100%;
    height: auto;
    border-radius: 8px;
    border: 2px solid var(--border-color);
    margin: 20px auto;
    display: block;
}
.image-placeholder {
    background-color: var(--given-cell-bg);
    border: 2px dashed var(--border-color);
    border-radius: 8px;
    padding: 30px;
    text-align: center;
    color: var(--footer-text-color);
    margin: 20px 0;
}

/* Footer Styles */
footer {
    position: fixed; bottom: 0; width: 100%; padding: 10px 0;
    background-color: var(--container-bg); border-top: 1px solid var(--border-color); text-align: center;
}
footer a { color: var(--footer-text-color); margin: 0 10px; text-decoration: none; }
footer a:hover { text-decoration: underline; }

/* Overlay Styles */
.board-overlay {
    position: absolute; top: 0; left: 0; width: 100%; height: 100%;
    display: flex; justify-content: center; align-items: center; text-align: center;
    font-weight: bold; z-index: 10;
}
#pregame-overlay { background-color: transparent; flex-direction: column; }
#pregame-content {
    background-color: var(--container-bg); padding: 30px 40px; border-radius: 10px;
    box-shadow: 0 5px 20px rgba(0,0,0,0.2); border: 1px solid var(--border-color);
}
#pregame-content h2 { font-size: clamp(1.5rem, 5vw, 2rem); }
#pregame-content p { font-size: clamp(0.9rem, 3vw, 1rem); font-weight: normal; }
#pause-overlay {
    background-color: rgba(255, 255, 255, 0.8); font-size: clamp(2rem, 10vw, 3rem);
    color: #333; cursor: not-allowed;
}
.dark-mode #pause-overlay { background-color: rgba(0, 0, 0, 0.8); color: #eee; }

#pause-btn { background-color: #ffc107; color: #212529; }
#pause-btn:hover { background-color: #e0a800; }

@media (min-width: 600px) {
    .page-container { padding: 20px 40px; }
    footer a { margin: 0 15px; }
}