:root {
    --neon-blue: #00f3ff;
    --neon-pink: #ff00ff;
    --neon-purple: #bd00ff;
    --neon-green: #00ff00;
    --bg-dark: #050510;
    --glass-bg: rgba(10, 10, 20, 0.85);
    --font-heading: 'Orbitron', sans-serif;
    --font-pixel: 'Press Start 2P', cursive;
}

body, html {
    margin: 0;
    padding: 0;
    width: 100%;
    height: 100%;
    overflow: hidden;
    font-family: var(--font-heading);
    background-color: var(--bg-dark);
    color: var(--neon-blue);
    user-select: none;
    background-image: 
        linear-gradient(rgba(0, 243, 255, 0.1) 1px, transparent 1px),
        linear-gradient(90deg, rgba(0, 243, 255, 0.1) 1px, transparent 1px);
    background-size: 50px 50px;
    background-position: center center;
}

#game-container {
    position: relative;
    width: 100%;
    height: 100%;
}

canvas {
    display: block;
}

#ui-layer {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
}

/* --- HUD Elements --- */

#score-block {
    position: absolute;
    top: 20px;
    left: 50%;
    transform: translateX(-50%);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 10px;
    background: var(--glass-bg);
    padding: 15px 30px;
    border: 2px solid var(--neon-blue);
    border-radius: 0 0 15px 15px;
    box-shadow: 0 0 15px var(--neon-blue);
    clip-path: polygon(10% 0, 90% 0, 100% 100%, 0% 100%);
}

#score-display, #money-display {
    font-family: var(--font-heading);
    font-size: 24px;
    font-weight: bold;
    text-shadow: 0 0 10px currentColor;
    letter-spacing: 2px;
}

#money-display {
    color: var(--neon-green); 
    font-size: 20px;
}

#high-score-display {
    position: absolute;
    top: 20px;
    left: 20px;
    font-size: 14px;
    background: var(--glass-bg);
    border: 1px solid var(--neon-purple);
    color: var(--neon-purple);
    padding: 8px 15px;
    border-radius: 5px;
    text-transform: uppercase;
    box-shadow: 0 0 10px var(--neon-purple);
}

#upgrade-btn {
    pointer-events: auto;
    position: absolute;
    bottom: 30px;
    right: 30px;
    padding: 15px 25px;
    background: rgba(0,0,0,0.8);
    color: var(--neon-pink);
    border: 2px solid var(--neon-pink);
    border-radius: 5px;
    cursor: pointer;
    font-family: var(--font-heading);
    font-size: 18px;
    text-transform: uppercase;
    transition: all 0.3s;
    box-shadow: 0 0 15px var(--neon-pink);
    touch-action: manipulation;
}

#upgrade-btn:hover, #upgrade-btn:active {
    background: var(--neon-pink);
    color: black;
    box-shadow: 0 0 25px var(--neon-pink);
}

/* --- Screens (Start, GameOver) --- */

.screen {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(5, 5, 10, 0.95);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    z-index: 10;
    backdrop-filter: blur(5px);
}

.hidden {
    display: none !important;
}

h1 {
    font-family: var(--font-pixel);
    font-size: 50px; 
    margin-bottom: 50px;
    color: var(--neon-blue);
    text-shadow: 
        3px 3px 0px var(--neon-pink),
        0 0 20px var(--neon-blue);
    text-align: center;
    line-height: 1.5;
}

.difficulty-select {
    display: flex;
    gap: 20px;
    flex-wrap: wrap;
    justify-content: center;
}

.diff-btn {
    padding: 15px 30px;
    font-family: var(--font-heading);
    font-size: 20px;
    cursor: pointer;
    background: transparent;
    border: 2px solid #fff;
    color: #fff;
    transition: all 0.2s;
    text-transform: uppercase;
    position: relative;
    overflow: hidden;
}

.diff-btn::before {
    content: '';
    position: absolute;
    top: 0; left: -100%;
    width: 100%; height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255,255,255,0.2), transparent);
    transition: 0.5s;
}

.diff-btn:hover::before {
    left: 100%;
}

.diff-btn[data-mode="easy"] { 
    border-color: var(--neon-green); 
    color: var(--neon-green); 
    box-shadow: 0 0 10px var(--neon-green);
}

.diff-btn[data-mode="medium"] { 
    border-color: var(--neon-blue); 
    color: var(--neon-blue);
    box-shadow: 0 0 10px var(--neon-blue);
}

.diff-btn[data-mode="nuclear"] { 
    border-color: #ff0000; 
    color: #ff0000;
    box-shadow: 0 0 20px #ff0000;
    animation: pulse-border 1.5s infinite alternate;
}

@keyframes pulse-border {
    from { box-shadow: 0 0 10px #ff0000; }
    to { box-shadow: 0 0 30px #ff0000; }
}

/* --- Upgrade Menu --- */

#upgrade-menu {
    position: absolute;
    right: 0;
    top: 0;
    bottom: 0;
    width: 350px; 
    max-width: 80vw;
    background: rgba(10, 15, 30, 0.98);
    border-left: 2px solid var(--neon-blue);
    padding: 20px;
    display: flex;
    flex-direction: column;
    gap: 20px;
    pointer-events: auto;
    z-index: 5;
    box-shadow: -10px 0 30px rgba(0, 243, 255, 0.2);
    overflow-y: auto;
}

#upgrade-menu h2 {
    color: var(--neon-pink);
    text-transform: uppercase;
    border-bottom: 2px solid var(--neon-pink);
    padding-bottom: 15px;
    margin-top: 40px; 
}

.upgrade-item {
    background: rgba(255, 255, 255, 0.05);
    padding: 20px;
    border: 1px solid var(--neon-blue);
    border-radius: 0;
    text-align: center;
    position: relative;
    clip-path: polygon(
        0 0, 100% 0, 
        100% calc(100% - 15px), calc(100% - 15px) 100%, 
        0 100%
    );
}

.progress-bar {
    width: 100%;
    height: 8px;
    background: #222;
    margin: 15px 0;
    border: 1px solid #444;
}

.progress-bar div {
    height: 100%;
    background: var(--neon-green);
    width: 0%;
    box-shadow: 0 0 10px var(--neon-green);
    transition: width 0.3s;
}

.upgrade-item button {
    background: transparent;
    border: 1px solid var(--neon-blue);
    color: var(--neon-blue);
    padding: 12px;
    width: 100%;
    text-transform: uppercase;
    font-family: var(--font-heading);
    font-weight: bold;
    letter-spacing: 1px;
    transition: 0.2s;
}

.upgrade-item button:active {
    background: var(--neon-blue);
    color: black;
}

.upgrade-item button:disabled {
    border-color: #444;
    color: #444;
}

/* --- Leaderboard --- */

#leaderboard-preview {
    margin-top: 30px;
    background: transparent;
    border: 1px solid var(--neon-purple);
    padding: 20px;
    width: 80%;
    max-width: 400px;
    box-shadow: 0 0 15px rgba(189, 0, 255, 0.2);
}

#leaderboard-preview h3 {
    color: var(--neon-purple);
    margin-top: 0;
}

#top-scores-list li {
    padding: 8px 0;
    border-bottom: 1px solid var(--neon-purple);
    font-family: 'Courier New', monospace;
    font-weight: bold;
}

/* Inputs */
input#player-name {
    background: transparent;
    border: 2px solid var(--neon-blue);
    color: white;
    padding: 12px;
    font-family: var(--font-heading);
    text-transform: uppercase;
    outline: none;
    width: 60%;
}

input#player-name:focus {
    box-shadow: 0 0 15px var(--neon-blue);
}

#restart-btn, #save-score-btn {
    padding: 15px 30px;
    font-size: 18px;
    background: var(--neon-blue);
    color: black;
    border: none;
    margin: 10px;
    font-family: var(--font-heading);
    font-weight: bold;
    text-transform: uppercase;
    cursor: pointer;
    box-shadow: 0 0 15px var(--neon-blue);
}

/* --- Mobile Queries --- */

@media (max-width: 768px) {
    h1 { font-size: 30px; }
    
    #score-block {
        top: 10px;
        padding: 5px 15px;
        width: 150px;
    }
    
    #score-display, #money-display {
        font-size: 16px;
    }
    
    #high-score-display {
        top: auto;
        bottom: 20px;
        left: 20px;
        font-size: 12px;
    }

    #upgrade-btn {
        bottom: 20px;
        right: 20px;
        padding: 10px 15px;
        font-size: 14px;
    }
    
    .difficulty-select {
        flex-direction: column;
        width: 80%;
    }
    
    .diff-btn {
        width: 100%;
        text-align: center;
    }

    #upgrade-menu {
        width: 100%;
        border-left: none;
        max-width: 100%;
    }
}