:root {
    --primary: #ff9900;
    --winner-glow: rgba(255,215,0,0.8);
    --box-size: 90px;
    --box-bg: linear-gradient(145deg,#ffcc66,#ff9900);
    --box-lid-bg: linear-gradient(145deg,#ffd699,#ffb866);
    --font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

body {
    font-family: var(--font-family);
    background: radial-gradient(circle at top, #ff9900, #141414);
    margin: 0;
    padding: 0;
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
}

#container {
    max-width: 520px;
    margin: 0 auto;
    padding: 20px;
    text-align: center;
    position: relative;
}

#couponForm {
    margin-bottom: 20px;
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    justify-content: center;
}

#couponInput {
    padding: 8px;
    font-size: 1.1em;
    border-radius: 5px;
    border: 1px solid #ccc;
    width: 180px;
    max-width: 50vw;
}

#checkBtn {
    padding: 8px 20px;
    font-size: 1.1em;
    border-radius: 5px;
    border: none;
    background: var(--primary);
    color: #fff;
    cursor: pointer;
}

#invalidMsg { color: #e74c3c; font-weight: bold; margin-top: 6px; width:100%; }
#successMsg { color: #27ae60; font-weight: bold; margin-top: 6px; width:100%; }

#boxes {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 12px;
    margin-top: 20px;
}

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


.box {
    width: var(--box-size);
    height: var(--box-size);
    position: relative;
    cursor: pointer;
    perspective: 600px;
    outline: none;
}

.box-inner {
    width: 100%;
    height: 100%;
    border-radius: 8px;
    background: var(--box-bg);
    box-shadow: 0 4px 8px rgba(0,0,0,0.2);
    position: relative;
    transition: transform 0.3s;
}

.box-lid {
    position: absolute;
    width: 100%;
    height: 40%;
    top: 0;
    left: 0;
    background: var(--box-lid-bg);
    border-radius: 8px 8px 0 0;
    transform-origin: top;
    transition: transform 0.5s;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: bold;
    font-size: 1.4em;
    color: #fff;
}

.box-front {
    width:100%;
    height:100%;
    display:flex;
    align-items:center;
    justify-content:center;
    font-size:2em;
    color:#fff;
}

.reward {
    position:absolute;
    top:50%;
    left:50%;
    transform:translate(-50%,-50%) scale(0.2);
    opacity:0;
    font-size:1.2em;
    font-weight:bold;
    color:#222;
    transition: transform 0.4s, opacity 0.4s;
}

.box:hover .box-inner {
    transform: translateY(-3px);
}
.box:active .box-inner {
    transform: translateY(1px);
}

.box.opened .box-lid {
    transform: rotateX(110deg) translateY(-4px);
}

.box.opened .reward {
    transform: translate(-50%,-50%) scale(1);
    opacity:1;
}

.box.opened {
    cursor: default;
}

.box.winner .box-inner {
    box-shadow: 0 0 15px 4px var(--winner-glow);
    border: 2px solid #f1c40f;
}

@media (max-width: 500px) {
    :root { --box-size: 72px; }
}

/* Confetti */
.confetti-piece {
    position: absolute;
    width: 8px;
    height: 8px;
    background: red;
    opacity: 0.8;
    animation: confetti-fall 1s forwards;
}
@keyframes confetti-fall {
    0% { transform: translateY(0) rotate(0deg); opacity:1; }
    100% { transform: translateY(60vh) rotate(360deg); opacity:0; }
}