* { 
    margin: 0; 
    padding: 0; 
    box-sizing: border-box; 
}

body {
    background: #0f172a;
    color: #fff;
    font-family: sans-serif;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    height: 100vh;
    overflow: hidden;
    position: relative;
}

#header {
    position: absolute;
    top: 5%;
    font-weight: 800;
    font-size: 38px;
    font-family: sans-serif;
}

canvas {
    border: 2px solid #0ea5e9;
    background: #1e293b;
}

#game-over, #start-screen {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    background: rgba(0, 0, 0, 0.85);
    padding: 30px 50px;
    border-radius: 12px;
    text-align: center;
    z-index: 20;
    line-height: 1.5;
}

#game-over p {
    font-size: 0.9rem;
}

.hidden { 
    display: none; 
}

.visible { 
    display: block !important; 
}

button {
    margin-top: 10px;
    padding: 10px 20px;
    font-size: 16px;
    background-color: #0ea5e9;
    color: white;
    border: none;
    border-radius: 6px;
    cursor: pointer;
    outline: none;
}

button:hover {
    background-color: #0284c7;
}

#wave-progress {
    position: absolute;
    top: 0;
    left: 0;
    height: 5px;
    background-color: #0284c7;
    z-index: 50;
    width: 0%;
    transition: width 0.1s ease;
}

.popup {
    position: absolute;
    top: 36%;
    left: 50%;
    transform: translate(-50%, -20%);
    background: rgb(0,0,0);
    padding: 20px 40px;
    border-radius: 12px;
    color: white;
    max-width: 400px;
    z-index: 100;
    display: none;
    line-height: 1.5;
}