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

body {
    font-family: Arial, sans-serif;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background-color: #f4f4f4;
}

/* Khung bao ngoài cùng */
.outer-frame {
    border: 2px solid #5b87c6;
    padding: 20px;
    background-color: #fff;
    width: 650px;
}

/* 1. BANNER: Đổi màu nền & Co giãn chữ */
.banner {
    text-align: center;
    font-weight: bold;
    padding: 15px 0;
    color: #000;
    margin-bottom: 40px;
    animation: animateBanner 4s infinite alternate ease-in-out;
}

@keyframes animateBanner {
    0% {
        background-color: #ff0055;
        font-size: 13px;
    }
    50% {
        background-color: #ff00ff;
        font-size: 18px;
    }
    100% {
        background-color: #00e5ff;
        font-size: 24px;
    }
}

/* Hàng chứa 4 khung */
.box-group {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 10px 20px 10px;
}

.box {
    width: 110px;
    height: 110px;
    display: flex;
    justify-content: center;
    align-items: center;
    font-weight: bold;
    font-size: 22px;
    color: #ffff00;
    text-shadow: 1px 1px 2px #000;
}

/* 2. Khung 1: Tự động thay đổi ảnh nền */
.box-1 {
    border: 3px solid red;
    background-size: cover;
    background-position: center;
    animation: changeBgImage 5s infinite ease-in-out;
}

@keyframes changeBgImage {
    0%, 45% {
        background-image: url('../images/2.jpg');
    }
    50%, 100% {
        background-image: url('../images/5.jpg');
    }
}

/* 3. Khung 2: Bo góc đối xưng & Viền nét đứt */
.box-2 {
    background-color: #00ffff;
    border: 3px dashed #0000ff;
    border-radius: 0 25px 0 25px;
}

/* 4. Khung 3: Bo góc ngược lại & Viền chấm bi */
.box-3 {
    background-color: #00ffff;
    border: 3px dotted #ff00ff;
    border-radius: 25px 0 25px 0;
}

/* 5. Khung 4: Xoay theo chiều kim đồng hồ */
.box-4 {
    background-color: #008080;
    border: 2px solid #7fff00;
    font-size: 14px;
    animation: rotateClockwise 6s linear infinite;
}

@keyframes rotateClockwise {
    from {
        transform: rotate(0deg);
    }
    to {
        transform: rotate(360deg);
    }
}