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

/* Kiểu dáng cho body */
body {
    font-family: Arial, sans-serif;
    line-height: 1.6;
    color: #333;
    background-color: #f4f4f9;
    margin-top: 100px;
    /* Để nội dung không che khuất header cố định */
}

/* Header */
#main-header {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    background-color: #0073e6;
    color: white;
    padding: 20px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    transition: all 0.3s;
    z-index: 1000;
}

/* Khi cuộn sẽ ẩn ảnh */
#main-header.scrolled {
    padding: 10px;
}

#header-content {
    display: flex;
    justify-content: space-between;
    width: 100%;
    align-items: center;
}

/* Bố trí tiêu đề và menu */
#header-left {
    display: flex;
    align-items: center;
}

#header-left h1 {
    margin-right: 15px;
    font-size: 1.5em;
}

#header-right ul {
    list-style-type: none;
    display: flex;
}

#header-right ul li {
    margin: 0 10px;
}

#header-right ul li a {
    color: white;
    text-decoration: none;
    font-weight: bold;
}

#header-right ul li a:hover {
    text-decoration: underline;
}

/* Ẩn ảnh khi cuộn */
#profile-picture {
    margin-left: 10px;
}

#profile-picture img {
    width: 50px;
    height: 50px;
    border-radius: 50%;
    transition: opacity 0.3s ease;
}

#main-header.scrolled #profile-picture img {
    opacity: 0;
    width: 0;
    height: 0;
}

/* Phần nội dung chính */
#content {
    margin: 20px;
    padding: 20px;
    background: #fff;
    border-radius: 8px;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

/* Footer */
footer {
    text-align: center;
    padding: 10px;
    background-color: #333;
    color: #fff;
    margin-top: 20px;
}

footer a {
    color: #0073e6;
    text-decoration: none;
}

footer a:hover {
    text-decoration: underline;
}