/* --- BỐ CỤC ĐẤU TRƯỜNG CUỐI KÌ --- */
.stadium-arena {
    height: 240px;
    background: linear-gradient(180deg, #1a237e 0%, #311b92 60%, #4a148c 100%); /* Bầu trời đêm vinh quang */
    box-shadow: inset 0 0 30px rgba(0,0,0,0.6);
    position: relative; 
    overflow: hidden;
    border-radius: 12px;
}

/* Khán đài mờ ảo phía sau */
.stadium-bg {
    position: absolute;
    top: 0; left: 0;
    width: 100%; height: 100%;
    background-image: 
        radial-gradient(2px 2px at 20px 30px, rgba(255,255,255,0.2), transparent),
        radial-gradient(2px 2px at 50px 70px, rgba(255,255,255,0.4), transparent),
        radial-gradient(3px 3px at 120px 40px, rgba(255,213,79,0.3), transparent),
        radial-gradient(2px 2px at 180px 110px, rgba(255,255,255,0.2), transparent);
    background-size: 100px 50px;
    z-index: 1;
}

/* Ánh đèn Spotlight rọi xuống bục */
.spotlight {
    position: absolute;
    top: -50px; left: 50%;
    transform: translateX(-50%);
    width: 200px; height: 300px;
    background: radial-gradient(ellipse at top, rgba(255, 255, 255, 0.4) 0%, rgba(255, 255, 255, 0) 70%);
    z-index: 2;
    pointer-events: none;
}

/* Bục vinh quang (Podium) */
.podium-base {
    position: absolute;
    bottom: 20px;
    left: 60%;
    transform: translateX(-50%);
    width: 120px;
    height: 30px;
    background: linear-gradient(to right, #ffd54f, #ff8f00, #ffd54f);
    border: 3px solid #ff6f00;
    border-radius: 10px 10px 0 0;
    box-shadow: 0 10px 15px rgba(0,0,0,0.6), inset 0 5px 10px rgba(255,255,255,0.5);
    z-index: 3;
    display: flex;
    justify-content: center;
}

/* Biểu tượng Toán học chiếu sáng trên bục */
.topic-icon {
    font-size: 3rem;
    position: absolute;
    bottom: 10px;
    animation: float-icon 2s ease-in-out infinite alternate;
}

@keyframes float-icon {
    0% { transform: translateY(0) scale(1); }
    100% { transform: translateY(-10px) scale(1.1); }
}

/* Nhân vật Học sinh Vô địch */
.student-champion {
    position: absolute;
    bottom: 20px; /* Đứng cạnh bục */
    left: 15%;
    font-size: 4.5rem;
    z-index: 5;
    filter: drop-shadow(0 5px 10px rgba(0,0,0,0.6));
}

/* Nhảy mừng cực mạnh khi làm đúng */
.happy-jump {
    animation: champion-jump 1s ease-out forwards !important;
}
@keyframes champion-jump {
    0% { transform: translateY(0); }
    40% { transform: translateY(-40px) scale(1.1) rotate(-10deg); }
    60% { transform: translateY(-40px) scale(1.1) rotate(10deg); }
    100% { transform: translateY(0) scale(1) rotate(0); }
}

/* Rung lắc khi làm sai */
.shake-error { animation: shake-char 0.4s !important; }
@keyframes shake-char {
    0% { transform: translateX(0); }
    25% { transform: translateX(-15px) rotate(-10deg); }
    50% { transform: translateX(15px) rotate(10deg); }
    75% { transform: translateX(-15px) rotate(-10deg); }
    100% { transform: translateX(0); }
}

/* Hiệu ứng Pháo hoa giấy (Confetti) rơi xuống */
.confetti-piece {
    position: absolute;
    top: -10px;
    width: 10px; height: 10px;
    opacity: 0.8;
    z-index: 6;
    animation: fall-down linear forwards;
}

@keyframes fall-down {
    0% { transform: translateY(0) rotate(0deg); opacity: 1; }
    100% { transform: translateY(250px) rotate(720deg); opacity: 0; }
}

.min-h-75 { min-height: 85px; }