:root {
    /* Color Palette */
    --bg-color: #f0f2f5;
    --container-bg: #ffffff;
    --h-menu-bg: #7FFFD4; /* Aquamarine base from image */
    --v-menu-bg: #3498db; /* Blue base from image */
    --accent-orange: #ff9800; /* Active/First item color in image */
    --hover-yellow: #ffeb3b;
    --text-dark: #2d3436;
    --text-light: #ffffff;
}

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

body {
    font-family: 'Inter', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-dark);
    line-height: 1.6;
    padding: 40px 20px;
    display: flex;
    flex-direction: column;
    align-items: center;
    min-height: 100vh;
}

h1 {
    margin-bottom: 40px;
    font-weight: 700;
    color: #1a1a1a;
    text-align: center;
}

.section {
    background: var(--container-bg);
    padding: 40px;
    border-radius: 20px;
    box-shadow: 0 15px 35px rgba(0, 0, 0, 0.05);
    margin-bottom: 30px;
    width: 100%;
    max-width: 800px;
    transition: transform 0.3s ease;
}

.section:hover {
    transform: translateY(-5px);
}

h2 {
    font-size: 1.2rem;
    margin-bottom: 25px;
    padding-bottom: 10px;
    border-bottom: 2px solid #eee;
    color: #555;
    text-transform: uppercase;
    letter-spacing: 1px;
}

/* --- 2.2.2 TẠO MENU NGANG --- */
.menu-ngang {
    list-style: none;
    display: flex;
    background-color: var(--h-menu-bg);
    padding: 5px;
    gap: 2px;
    width: fit-content;
}

.menu-ngang li {
    padding: 12px 25px;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    color: #333;
    font-weight: 400;
}

/* First item like in screenshot (Orange) */
.menu-ngang li:first-child {
    background-color: var(--accent-orange);
    color: white;
    font-weight: bold;
}

/* REQUIRED: Menu Ngang Hover effect */
.menu-ngang li:hover {
    background-color: var(--hover-yellow) !important;
    border-radius: 5px;
    font-weight: bold !important;
    color: #000;
}

/* --- 2.2.3 TẠO MENU DỌC --- */
.menu-doc {
    list-style: none;
    width: 280px;
    background-color: var(--v-menu-bg);
    overflow: hidden;
    border: 1px solid rgba(0,0,0,0.1);
}

.menu-doc li {
    padding: 15px 25px;
    color: var(--text-light);
    border-bottom: 1px solid rgba(255, 255, 255, 0.3);
    cursor: pointer;
    transition: all 0.3s ease;
    position: relative;
}

.menu-doc li:last-child {
    border-bottom: none;
}

/* REQUIRED: Menu Doc Hover effect */
.menu-doc li:hover {
    /* "làm sáng màu nền xanh dương (130%)" */
    background-color: #3498db; 
    filter: brightness(1.3);
    font-style: italic;
    padding-left: 35px; /* Subtle premium micro-animation */
}

/* Responsive Design */
@media (max-width: 600px) {
    .menu-ngang {
        flex-direction: column;
        width: 100%;
    }
    .menu-doc {
        width: 100%;
    }
}