/* Định dạng toàn cục */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background: linear-gradient(135deg, #1a1a2e, #16213e, #0f3460);
    font-family: 'Arial', sans-serif;
}

.container {
    text-align: center;
    background: rgba(255, 255, 255, 0.05);
    padding: 30px;
    border-radius: 30px;
    backdrop-filter: blur(10px);
    box-shadow: 0 25px 50px rgba(0,0,0,0.8);
    border: 1px solid rgba(255,255,255,0.1);
}

h1 {
    color: #e94560;
    font-size: 3rem;
    text-shadow: 0 0 20px rgba(233, 69, 96, 0.6);
    margin-bottom: 15px;
    letter-spacing: 4px;
}

.trang_thai {
    color: #eee;
    font-size: 1.5rem;
    padding: 10px;
    margin-bottom: 20px;
    background: rgba(0,0,0,0.4);
    border-radius: 15px;
    border-left: 5px solid #e94560;
    transition: 0.3s;
}

.ban_co {
    display: grid;
    grid-template-columns: repeat(3, 120px);
    grid-template-rows: repeat(3, 120px);
    gap: 12px;
    background: transparent;
    justify-content: center;
    margin: 10px auto;
}

/* Ô cờ - hiệu ứng 3D và bóng đổ */
.o {
    background: rgba(255, 255, 255, 0.08);
    border: 2px solid rgba(255, 255, 255, 0.15);
    border-radius: 20px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 4.5rem;
    font-weight: 900;
    color: white;
    cursor: pointer;
    transition: all 0.25s cubic-bezier(0.175, 0.885, 0.32, 1.275);
    box-shadow: 0 8px 0 rgba(0,0,0,0.4), inset 0 -3px 0 rgba(255,255,255,0.1);
    text-shadow: 0 0 25px currentColor;
}

.o:hover {
    transform: translateY(-5px) scale(1.03);
    background: rgba(255, 255, 255, 0.18);
    border-color: rgba(255,255,255,0.5);
    box-shadow: 0 15px 30px rgba(0,0,0,0.6);
}

/* Hiệu ứng cho X và X */
.o.khac_x {
    color: #00d2ff;
    text-shadow: 0 0 30px #00d2ff, 0 0 60px #00d2ff66;
    animation: no_ra_x 0.3s ease-out;
}

.o.khac_o {
    color: #ff6b6b;
    text-shadow: 0 0 30px #ff6b6b, 0 0 60px #ff6b6b66;
    animation: no_ra_o 0.3s ease-out;
}

/* Hiệu ứng xuất hiện khi đánh dấu */
@keyframes no_ra_x {
    0% { transform: scale(0) rotate(-90deg); opacity: 0; }
    100% { transform: scale(1) rotate(0deg); opacity: 1; }
}

@keyframes no_ra_o {
    0% { transform: scale(0) rotate(90deg) skew(10deg); opacity: 0; }
    100% { transform: scale(1) rotate(0deg) skew(0deg); opacity: 1; }
}

/* Hiệu ứng nhấp nháy khi thắng */
.o.chien_thang {
    animation: nhap_nhay_thang 0.8s infinite alternate;
    border-color: #ffd700;
    box-shadow: 0 0 40px #ffd70088;
}

@keyframes nhap_nhay_thang {
    0% { transform: scale(1); background: rgba(255, 215, 0, 0.2); }
    100% { transform: scale(1.08); background: rgba(255, 215, 0, 0.5); }
}

.nut_dat_lai {
    margin-top: 25px;
    padding: 14px 45px;
    font-size: 1.3rem;
    font-weight: bold;
    color: #fff;
    background: #e94560;
    border: none;
    border-radius: 50px;
    cursor: pointer;
    transition: all 0.3s;
    box-shadow: 0 8px 0 #a02040, 0 10px 30px rgba(233, 69, 96, 0.4);
    letter-spacing: 2px;
}

.nut_dat_lai:hover {
    transform: translateY(-3px);
    box-shadow: 0 12px 0 #a02040, 0 20px 40px rgba(233, 69, 96, 0.6);
}

.nut_dat_lai:active {
    transform: translateY(5px);
    box-shadow: 0 3px 0 #a02040;
}

/* Responsive cho mobile */
@media (max-width: 480px) {
    .ban_co {
        grid-template-columns: repeat(3, 85px);
        grid-template-rows: repeat(3, 85px);
        gap: 8px;
    }
    .o {
        font-size: 3rem;
        border-radius: 15px;
    }
    h1 { font-size: 2.2rem; }
    .trang_thai { font-size: 1.1rem; }
}