:root {
    --bg-color: #0b0819;
    --grid-bg: rgba(18, 14, 38, 0.7);
    --cell-empty: rgba(255, 255, 255, 0.04);
    --cell-border: rgba(255, 255, 255, 0.06);
    --primary: #a855f7;
    --secondary: #00f0ff;
    --accent-red: #ff0055;
    --text-color: #ffffff;

    /* Neon Palette for blocks */
    --color-1: #ff0055;
    --color-2: #00f0ff;
    --color-3: #00ff66;
    --color-4: #ffee00;
    --color-5: #aa00ff;
    --color-6: #ff8800;

    --gap: 6px;
    --cell-size: 42px;

    --glass-bg: rgba(255, 255, 255, 0.05);
    --glass-border: rgba(255, 255, 255, 0.12);
    --glass-shadow: 0 12px 40px rgba(0, 0, 0, 0.5);
    --glass-blur: blur(20px);
}

* {
    box-sizing: border-box;
    user-select: none;
    -webkit-user-select: none;
}

html, body {
    margin: 0;
    padding: 0;
    width: 100%;
    height: 100%;
    height: 100dvh;
    font-family: 'Outfit', -apple-system, BlinkMacSystemFont, sans-serif;
    background: radial-gradient(circle at 50% 20%, #1e133e 0%, #0d0822 50%, #05030f 100%);
    background-attachment: fixed;
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    overflow: hidden;
    touch-action: none;
    overscroll-behavior: none;
    -webkit-tap-highlight-color: transparent;
}

/* Dynamic ambient glow behind app */
body::before {
    content: '';
    position: fixed;
    width: 500px;
    height: 500px;
    background: radial-gradient(circle, rgba(168, 85, 247, 0.15) 0%, rgba(0, 240, 255, 0.05) 50%, transparent 70%);
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    pointer-events: none;
    z-index: 0;
    filter: blur(40px);
}

#app {
    position: relative;
    z-index: 1;
    width: 100%;
    max-width: 960px;
    padding: 20px;
    height: 100%;
    max-height: 100dvh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
}

/* Layout Wrapper */
.layout-wrapper {
    display: flex;
    gap: 40px;
    align-items: flex-start;
    justify-content: center;
    width: 100%;
}

.left-column {
    display: flex;
    flex-direction: column;
    gap: 20px;
    width: 250px;
    align-items: center;
}

.game-logo {
    width: 100%;
    max-width: 220px;
    height: auto;
    object-fit: contain;
    filter: drop-shadow(0 0 20px rgba(0, 240, 255, 0.5)) drop-shadow(0 0 40px rgba(168, 85, 247, 0.3));
    transition: transform 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.game-logo:hover {
    transform: scale(1.04) rotate(-1deg);
}

/* Sidebar Leaderboard */
.sidebar {
    width: 100%;
    background: var(--glass-bg);
    backdrop-filter: var(--glass-blur);
    -webkit-backdrop-filter: var(--glass-blur);
    padding: 20px;
    border-radius: 20px;
    height: 340px;
    overflow-y: auto;
    border: 1px solid var(--glass-border);
    box-shadow: var(--glass-shadow);
}

.sidebar-header {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    border-bottom: 1px solid var(--glass-border);
    padding-bottom: 12px;
    margin-bottom: 15px;
}

.sidebar-header .trophy-icon {
    font-size: 1.2rem;
    filter: drop-shadow(0 0 8px #ffee00);
}

.sidebar h3 {
    margin: 0;
    font-size: 0.95rem;
    font-weight: 700;
    letter-spacing: 1.5px;
    color: var(--secondary);
}

#high-score-list {
    list-style: none;
    padding: 0;
    margin: 0;
}

#high-score-list li {
    background: rgba(255, 255, 255, 0.03);
    margin-bottom: 10px;
    padding: 10px 14px;
    border-radius: 12px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 0.9rem;
    color: #e2e8f0;
    border: 1px solid rgba(255, 255, 255, 0.05);
    transition: transform 0.2s, background-color 0.2s;
}

#high-score-list li:hover {
    transform: translateX(4px);
    background: rgba(255, 255, 255, 0.07);
}

/* Leaderboard Ranking Badges */
#high-score-list li:nth-child(1) {
    background: linear-gradient(90deg, rgba(255, 238, 0, 0.15), rgba(255, 136, 0, 0.05));
    border-color: rgba(255, 238, 0, 0.4);
    color: #ffee00;
    font-weight: bold;
    box-shadow: 0 0 15px rgba(255, 238, 0, 0.15);
}

#high-score-list li:nth-child(2) {
    background: linear-gradient(90deg, rgba(255, 255, 255, 0.15), rgba(200, 200, 255, 0.05));
    border-color: rgba(220, 220, 255, 0.3);
    color: #e2e8f0;
}

#high-score-list li:nth-child(3) {
    background: linear-gradient(90deg, rgba(205, 127, 50, 0.15), rgba(150, 80, 20, 0.05));
    border-color: rgba(205, 127, 50, 0.3);
    color: #cd7f32;
}

.sidebar::-webkit-scrollbar {
    width: 5px;
}

.sidebar::-webkit-scrollbar-thumb {
    background: rgba(255, 255, 255, 0.15);
    border-radius: 4px;
}

/* Game Area Layout */
.game-area {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 20px;
    flex: 1;
    max-width: 480px;
}

/* Header & Score Cards */
.game-header {
    display: flex;
    gap: 15px;
    width: 100%;
    justify-content: center;
}

.score-card {
    background: var(--glass-bg);
    backdrop-filter: var(--glass-blur);
    -webkit-backdrop-filter: var(--glass-blur);
    border: 1px solid var(--glass-border);
    padding: 10px 24px;
    border-radius: 16px;
    text-align: center;
    min-width: 120px;
    box-shadow: var(--glass-shadow);
    transition: transform 0.2s, box-shadow 0.2s;
}

.score-card:hover {
    transform: translateY(-2px);
    border-color: rgba(255, 255, 255, 0.25);
}

.score-card.main-score {
    background: linear-gradient(135deg, rgba(168, 85, 247, 0.15), rgba(0, 240, 255, 0.15));
    border-color: rgba(0, 240, 255, 0.3);
}

.score-label {
    font-size: 0.68rem;
    color: #94a3b8;
    letter-spacing: 2px;
    font-weight: 700;
    margin-bottom: 2px;
}

#score, #high-score-display {
    font-size: 1.5rem;
    font-weight: 800;
    color: #ffffff;
    text-shadow: 0 0 12px rgba(255, 255, 255, 0.3);
}

#score {
    background: linear-gradient(90deg, #00f0ff, #a855f7);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

/* Main Board Container */
#game-container {
    background: var(--grid-bg);
    backdrop-filter: var(--glass-blur);
    -webkit-backdrop-filter: var(--glass-blur);
    padding: 14px;
    border-radius: 24px;
    border: 1px solid var(--glass-border);
    box-shadow: 0 20px 50px rgba(0, 0, 0, 0.6), inset 0 0 20px rgba(255, 255, 255, 0.02);
}

#grid-container {
    display: grid;
    grid-template-columns: repeat(8, 1fr);
    grid-template-rows: repeat(8, 1fr);
    gap: var(--gap);
    width: calc(8 * var(--cell-size) + 7 * var(--gap));
    height: calc(8 * var(--cell-size) + 7 * var(--gap));
}

.cell {
    width: var(--cell-size);
    height: var(--cell-size);
    background-color: var(--cell-empty);
    border: 1px solid var(--cell-border);
    border-radius: 8px;
    transition: background-color 0.15s ease, transform 0.15s ease, box-shadow 0.15s ease;
}

.cell.filled {
    border-color: rgba(255, 255, 255, 0.3);
    box-shadow: inset 0 0 10px rgba(255, 255, 255, 0.4), 0 0 12px currentColor;
}

.cell.clearing {
    animation: clearFlash 0.35s cubic-bezier(0.1, 0.9, 0.2, 1) forwards;
    z-index: 10;
}

@keyframes clearFlash {
    0% {
        transform: scale(1);
        filter: brightness(1);
    }
    50% {
        transform: scale(1.15);
        filter: brightness(2.5) drop-shadow(0 0 15px white);
        background-color: #ffffff !important;
    }
    100% {
        transform: scale(0);
        filter: brightness(3);
        opacity: 0;
    }
}

/* Piece Tray Container */
.piece-tray-wrapper {
    width: 100%;
    background: var(--glass-bg);
    backdrop-filter: var(--glass-blur);
    -webkit-backdrop-filter: var(--glass-blur);
    border: 1px solid var(--glass-border);
    border-radius: 20px;
    padding: 12px 16px;
    box-shadow: var(--glass-shadow);
    display: flex;
    flex-direction: column;
    align-items: center;
}

.tray-label {
    font-size: 0.65rem;
    color: #64748b;
    letter-spacing: 2px;
    font-weight: 700;
    margin-bottom: 8px;
}

#piece-container {
    display: flex;
    justify-content: space-evenly;
    align-items: center;
    gap: 15px;
    width: 100%;
    height: 100px;
}

.piece-preview {
    display: grid;
    gap: 3px;
    cursor: grab;
    transition: transform 0.2s cubic-bezier(0.175, 0.885, 0.32, 1.275), filter 0.2s;
    padding: 6px;
    border-radius: 10px;
    background: rgba(255, 255, 255, 0.02);
}

.piece-preview:hover {
    transform: scale(1.08);
    background: rgba(255, 255, 255, 0.05);
}

.piece-preview:active {
    cursor: grabbing;
    transform: scale(1.15);
}

.piece-cell {
    width: 22px;
    height: 22px;
    border-radius: 5px;
    pointer-events: none;
}

/* Draggable Visual Helper */
.dragging-clone {
    position: fixed;
    pointer-events: none;
    z-index: 1000;
    opacity: 0.95;
    transform: scale(1.08) translateY(-4px) !important;
    filter: drop-shadow(0 12px 25px rgba(0, 0, 0, 0.7)) drop-shadow(0 0 15px rgba(0, 240, 255, 0.4));
    transition: filter 0.15s ease;
}

/* Top Nav Buttons (Settings & Leaderboard) */
.top-nav-buttons {
    position: absolute;
    top: 20px;
    right: 20px;
    display: flex;
    gap: 12px;
    z-index: 1000;
}

#settings-btn,
#leaderboard-btn {
    background: var(--glass-bg);
    backdrop-filter: var(--glass-blur);
    -webkit-backdrop-filter: var(--glass-blur);
    border: 1px solid var(--glass-border);
    color: var(--secondary);
    width: 46px;
    height: 46px;
    border-radius: 50%;
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    transition: all 0.2s cubic-bezier(0.175, 0.885, 0.32, 1.275);
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.3);
}

#leaderboard-btn {
    color: var(--color-4);
}

#settings-btn:hover,
#leaderboard-btn:hover {
    background: rgba(255, 255, 255, 0.15);
    transform: scale(1.1);
    box-shadow: 0 0 20px rgba(0, 240, 255, 0.4);
}

/* Modals & Overlays */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(5, 3, 15, 0.85);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 2000;
    opacity: 1;
    transition: opacity 0.3s ease;
}

.modal.hidden {
    opacity: 0;
    pointer-events: none;
}

.modal-content {
    background: linear-gradient(145deg, rgba(25, 18, 50, 0.95), rgba(12, 8, 30, 0.95));
    border: 1px solid var(--glass-border);
    padding: 36px 40px;
    border-radius: 24px;
    text-align: center;
    box-shadow: 0 0 50px rgba(168, 85, 247, 0.3), var(--glass-shadow);
    transform: scale(1);
    transition: transform 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275);
    max-width: 420px;
    width: 90%;
}

.modal.hidden .modal-content {
    transform: scale(0.85);
}

.modal h2 {
    margin: 0 0 10px 0;
    font-size: 2.2rem;
    background: linear-gradient(90deg, #ff0055, #ffee00);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    font-weight: 800;
    letter-spacing: 2px;
}

.modal p {
    color: #94a3b8;
    margin: 5px 0 0 0;
    font-size: 0.85rem;
    letter-spacing: 2px;
}

#final-score {
    font-size: 3.2rem;
    font-weight: 800;
    color: #ffffff;
    margin: 10px 0 25px 0;
    text-shadow: 0 0 20px rgba(0, 240, 255, 0.5);
}

/* Action Buttons */
#restart-btn,
#close-settings-btn,
#close-leaderboard-btn,
#submit-score-btn {
    background: linear-gradient(90deg, var(--secondary), var(--primary));
    color: #0b0819;
    border: none;
    padding: 14px 36px;
    font-size: 1.05rem;
    font-weight: 800;
    letter-spacing: 1px;
    border-radius: 50px;
    cursor: pointer;
    transition: transform 0.2s, box-shadow 0.2s;
    font-family: inherit;
}

#restart-btn:hover,
#close-settings-btn:hover,
#close-leaderboard-btn:hover,
#submit-score-btn:hover {
    transform: scale(1.05);
    box-shadow: 0 0 25px rgba(0, 240, 255, 0.6);
}

#restart-btn:active,
#close-settings-btn:active,
#close-leaderboard-btn:active,
#submit-score-btn:active {
    transform: scale(0.96);
}

/* Settings Controls */
.settings-group {
    margin: 20px 0;
    text-align: left;
}

.toggle-label {
    display: flex;
    align-items: center;
    justify-content: space-between;
    cursor: pointer;
    font-size: 1rem;
    color: #e2e8f0;
    margin-bottom: 15px;
}

.toggle-label input[type="checkbox"] {
    cursor: pointer;
    width: 20px;
    height: 20px;
    accent-color: var(--secondary);
}

/* All Clear Overlay */
.overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    z-index: 3000;
    opacity: 0;
    transition: opacity 0.3s;
}

.overlay.visible {
    opacity: 1;
}

.all-clear-text {
    font-size: 4rem;
    font-weight: 800;
    color: #fff;
    text-shadow: 0 0 20px var(--color-4), 0 0 40px var(--color-4);
    transform: scale(0);
    animation: popIn 0.5s cubic-bezier(0.175, 0.885, 0.32, 1.275) forwards;
}

.all-clear-sub {
    font-size: 2rem;
    color: var(--color-3);
    font-weight: bold;
    margin-top: 10px;
    opacity: 0;
    animation: slideUp 0.5s 0.2s forwards;
}

@keyframes popIn {
    0% { transform: scale(0) rotate(-10deg); }
    70% { transform: scale(1.2) rotate(5deg); }
    100% { transform: scale(1) rotate(0); }
}

@keyframes slideUp {
    0% { opacity: 0; transform: translateY(20px); }
    100% { opacity: 1; transform: translateY(0); }
}

/* ==========================================================================
   Responsive Mobile Optimization (Smartphones & Tablets <= 820px)
   ========================================================================== */
@media (max-width: 820px) {
    :root {
        --gap: 4px;
        --cell-size: min(40px, calc((100vw - 50px) / 8 - 4px), calc((100dvh - 250px) / 8 - 4px));
    }

    #app {
        padding: 10px 12px;
        justify-content: space-between;
        height: 100dvh;
        max-height: 100dvh;
    }

    .top-nav-buttons {
        top: 12px;
        right: 12px;
        gap: 8px;
    }

    #settings-btn,
    #leaderboard-btn {
        width: 40px;
        height: 40px;
    }

    .layout-wrapper {
        flex-direction: column;
        align-items: center;
        gap: 12px;
        margin-top: 0;
        width: 100%;
        height: 100%;
        justify-content: flex-start;
    }

    .left-column {
        width: 100%;
        max-width: 320px;
        flex-direction: row;
        justify-content: center;
        align-items: center;
        padding: 0;
        margin-top: 2px;
    }

    .game-logo {
        max-width: 200px;
    }

    .sidebar {
        display: none; /* Leaderboard is accessible via top-right nav button on mobile */
    }

    .game-area {
        width: 100%;
        max-width: 100%;
        gap: 12px;
        padding: 0;
    }

    .game-header {
        gap: 10px;
    }

    .score-card {
        padding: 6px 16px;
        min-width: 95px;
        border-radius: 12px;
    }

    .score-label {
        font-size: 0.6rem;
    }

    #score, #high-score-display {
        font-size: 1.25rem;
    }

    #game-container {
        padding: 8px;
        border-radius: 18px;
    }

    .piece-tray-wrapper {
        padding: 8px 12px;
        border-radius: 16px;
    }

    .tray-label {
        font-size: 0.6rem;
        margin-bottom: 4px;
    }

    #piece-container {
        height: 85px;
        gap: 10px;
    }

    .piece-preview {
        transform: scale(0.85);
    }
}

/* Extra small screens (height <= 660px) */
@media (max-height: 660px) {
    :root {
        --cell-size: min(32px, calc((100dvh - 210px) / 8 - 4px));
    }

    .game-logo {
        max-width: 130px;
    }

    .game-area {
        gap: 6px;
    }

    #piece-container {
        height: 75px;
    }

    .piece-preview {
        transform: scale(0.75);
    }
}