:root {
    --bg-color: #e1f5fe;
    /* Soft light blue */
    --primary-color: #03a9f4;
    /* Bright blue */
    --secondary-color: #ffca28;
    /* Cheerful yellow */
    --accent-color: #ff5252;
    /* Red accent */
    --text-color: #37474f;
    /* Dark slate */
    --board-bg: #ffffff;
    --tray-bg: #b3e5fc;
    --success-color: #00e676;
    /* Green */
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: 'Nunito', sans-serif;
    user-select: none;
    -webkit-user-drag: none;
    /* Prevent default image dragging */
}

body {
    background-color: var(--bg-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    overflow: hidden;
    /* Prevent scrolling when dragging */
}

/* --- Start Menu Overlay --- */
.menu-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(225, 245, 254, 0.95);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 2000;
}

.menu-overlay.hidden {
    display: none;
}

.menu-content {
    background-color: var(--board-bg);
    padding: 30px;
    border-radius: 30px;
    text-align: center;
    box-shadow: 0 15px 40px rgba(0, 0, 0, 0.15);
    border: 8px solid var(--primary-color);
    max-width: 800px;
    width: 95%;
    max-height: 95vh;
    overflow-y: auto;
}

.menu-content h1 {
    font-size: 3rem;
    color: var(--primary-color);
    margin-bottom: 5px;
    text-shadow: 2px 2px 0px rgba(0, 0, 0, 0.1);
}

.menu-content h2 {
    font-size: 1.5rem;
    color: #666;
    margin-bottom: 20px;
}

/* Puzzle Image Selector */
.puzzle-selector {
    margin-bottom: 20px;
}

.thumbnails {
    display: flex;
    justify-content: center;
    gap: 15px;
    margin-top: 10px;
}

.thumbnail-wrapper {
    position: relative;
    width: 120px;
    height: 120px;
    border-radius: 12px;
    overflow: hidden;
    cursor: pointer;
    border: 4px solid transparent;
    transition: transform 0.2s;
}

.thumbnail-wrapper:hover {
    transform: scale(1.05);
}

.thumbnail-wrapper.selected {
    border-color: var(--accent-color);
    box-shadow: 0 4px 10px rgba(255, 82, 82, 0.4);
    transform: scale(1.1);
}

.thumbnail {
    width: 100%;
    height: 100%;
    background-size: cover;
    background-position: center;
}

.thumbnail-wrapper.locked .thumbnail {
    filter: grayscale(100%) blur(2px);
    opacity: 0.7;
}

.lock-icon {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    font-size: 2rem;
    color: #fff;
    text-shadow: 0 2px 4px rgba(0, 0, 0, 0.5);
    display: none;
}

.thumbnail-wrapper.locked .lock-icon {
    display: block;
}

/* Difficulty Selector */
.difficulty-selector {
    margin-bottom: 20px;
    background: var(--bg-color);
    padding: 15px;
    border-radius: 16px;
}

.diff-buttons {
    display: flex;
    justify-content: center;
    gap: 10px;
    margin-top: 10px;
}

.diff-btn {
    background-color: #fff;
    border: 3px solid #ccc;
    border-radius: 16px;
    padding: 10px;
    font-size: 1.1rem;
    font-weight: 700;
    cursor: pointer;
    flex: 1;
    min-width: 120px;
    transition: all 0.2s;
}

.diff-btn small {
    display: block;
    font-size: 0.85rem;
    color: #888;
    margin-top: 5px;
}

.diff-btn.selected {
    background-color: var(--secondary-color);
    border-color: var(--secondary-color);
    box-shadow: 0 4px 0 #f57f17;
    transform: translateY(-2px);
}

.diff-btn.selected small {
    color: #555;
}

/* Buttons & Toggles */
.sound-toggle-container {
    margin-bottom: 20px;
    font-size: 1.2rem;
    font-weight: bold;
}

.btn {
    background-color: var(--success-color);
    color: #111;
    border: none;
    border-radius: 50px;
    padding: 12px 24px;
    font-size: 1.2rem;
    font-weight: 800;
    cursor: pointer;
    box-shadow: 0 6px 0 #00b0ff;
    transition: all 0.1s;
}

.btn:active {
    transform: translateY(6px);
    box-shadow: 0 0 0 transparent;
}

.btn-start {
    font-size: 1.8rem;
    padding: 15px 50px;
    background-color: var(--success-color);
    box-shadow: 0 6px 0 #00c853;
}

.btn-secondary {
    background-color: var(--secondary-color);
    box-shadow: 0 6px 0 #f57f17;
    font-size: 1rem;
    padding: 10px 20px;
}

.btn-danger {
    background-color: var(--accent-color);
    color: white;
    box-shadow: 0 6px 0 #d50000;
}

/* --- Main Game Area --- */
.game-container {
    width: 100vw;
    height: 100vh;
    display: flex;
    flex-direction: column;
    padding: 10px;
    max-width: 1000px;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: white;
    padding: 10px 20px;
    border-radius: 16px;
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.05);
    margin-bottom: 10px;
    flex-wrap: wrap;
    gap: 10px;
}

header h1 {
    font-size: 1.8rem;
    color: var(--primary-color);
}

.stats-panel {
    display: flex;
    gap: 15px;
}

.stat-box {
    display: flex;
    flex-direction: column;
    align-items: center;
    background: var(--bg-color);
    padding: 5px 15px;
    border-radius: 10px;
    font-weight: bold;
}

.stat-value {
    font-size: 1.3rem;
    color: var(--accent-color);
}

.progress-bar-container {
    flex-grow: 1;
    min-width: 200px;
    margin: 0 15px;
}

.progress-text {
    font-size: 0.9rem;
    font-weight: 700;
    margin-bottom: 3px;
    text-transform: uppercase;
}

.progress-bar {
    height: 12px;
    background-color: #eee;
    border-radius: 6px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    width: 0%;
    background-color: var(--success-color);
    transition: width 0.3s ease;
}

/* Board constraints */
.game-board {
    flex-grow: 1;
    display: flex;
    flex-direction: column;
    gap: 10px;
    min-height: 0;
    /* Important for flex child */
}

/* Target Area */
.puzzle-grid {
    flex-shrink: 0;
    margin: 0 auto;
    background-color: rgba(255, 255, 255, 0.5);
    border: 4px dashed rgba(0, 0, 0, 0.2);
    border-radius: 8px;
    position: relative;
    /* Aspect ratio will be maintained via JS setting width/height */
}

/* Individual Slot (Placeholder) */
.puzzle-slot {
    position: absolute;
    box-sizing: border-box;
    border: 1px dotted rgba(0, 0, 0, 0.1);
}

/* Piece Tray Area */
.pieces-tray {
    flex-grow: 1;
    background-color: var(--tray-bg);
    border-radius: 16px;
    padding: 10px;
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    align-content: flex-start;
    gap: 10px;
    overflow-y: auto;
    box-shadow: inset 0 0 10px rgba(0, 0, 0, 0.1);
}

/* A draggable puzzle piece */
.puzzle-piece {
    position: absolute;
    cursor: grab;
    background-repeat: no-repeat;
    box-shadow: 2px 2px 8px rgba(0, 0, 0, 0.3);
    border-radius: 4px;
    /* Optional slight rounding */
    touch-action: none;
    /* Required for pointer events */
    transition: transform 0.1s, box-shadow 0.1s;
    z-index: 10;
}

.puzzle-piece:active,
.puzzle-piece.dragging {
    cursor: grabbing;
    transform: scale(1.05);
    box-shadow: 5px 5px 15px rgba(0, 0, 0, 0.4);
    z-index: 100;
}

.puzzle-piece.placed {
    cursor: default;
    box-shadow: none;
    border-radius: 0;
    /* Perfect fit */
    z-index: 1;
}

/* Modals */
.modal {
    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: 3000;
}

.modal.hidden {
    display: none;
}

.modal-content {
    background-color: white;
    padding: 40px;
    border-radius: 20px;
    text-align: center;
    border: 6px solid var(--secondary-color);
}

.modal-content h2 {
    font-size: 2.5rem;
    color: var(--primary-color);
    margin-bottom: 10px;
}

.highlight {
    color: var(--accent-color);
    font-size: 1.5rem;
    font-weight: 900;
}

/* Animations */
.bounce {
    animation: bounceObj 2s infinite ease-in-out;
}

@keyframes bounceObj {

    0%,
    100% {
        transform: translateY(0);
    }

    50% {
        transform: translateY(-10px);
    }
}

.timer-alert {
    color: var(--accent-color);
    animation: flash 1s infinite;
}

@keyframes flash {

    0%,
    100% {
        opacity: 1;
    }

    50% {
        opacity: 0.5;
    }
}

/* Back to Hub Button */
.btn-back-hub {
    position: absolute;
    top: 20px;
    left: 20px;
    background-color: #ff6b6b;
    color: white;
    text-decoration: none;
    padding: 10px 20px;
    border-radius: 50px;
    font-weight: bold;
    font-size: 1.1rem;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    transition: all 0.2s;
    z-index: 9999;
}

.btn-back-hub:hover {
    transform: scale(1.05);
    box-shadow: 0 6px 12px rgba(0, 0, 0, 0.15);
}

/* --- Responsive Adjustments --- */
@media (max-width: 600px) {
    .menu-overlay {
        align-items: flex-start;
        padding-top: 70px;
        padding-bottom: 20px;
        overflow-y: auto;
    }

    .menu-content {
        margin: auto;
        padding: 20px;
        width: 95%;
    }

    .menu-content h1 {
        font-size: 2.2rem;
    }

    .menu-content h2 {
        font-size: 1.2rem;
    }

    .thumbnails {
        flex-wrap: wrap;
        gap: 10px;
    }

    .thumbnail-wrapper {
        width: 80px;
        height: 80px;
    }

    .diff-buttons {
        flex-direction: column;
        align-items: center;
    }

    .diff-btn {
        width: 100%;
        margin-bottom: 5px;
    }

    .btn-back-hub {
        top: 10px;
        left: 10px;
        font-size: 0.9rem;
        padding: 8px 15px;
    }
}

@media (max-height: 700px) {
    .menu-overlay {
        align-items: flex-start;
        padding-top: 70px;
        padding-bottom: 20px;
        overflow-y: auto;
    }

    .menu-content {
        margin: auto;
    }
}