header {
    background-color: #111827;
    color: white;
    display: flex;
    flex-direction: column;  
    justify-content: center;
    align-items: center;
    padding: 20px 30px;     
    text-align: center;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.2);
}

header h1 {
    margin: 0;
    font-size: 22px;
}

header p {
    margin: 8px 0 0 0;  
    font-size: 14px;
    color: #d1d5db;
}

body {
    margin: 0;
    font-family: 'Segoe UI', sans-serif;
    background: #f0f4f8;
}

.container {
    display: flex;
    min-height: 90vh;
}

.sidebar {
    width: 250px;
    background-color: #1f2937;
    color: white;
    padding: 20px;
    box-shadow: 2px 0 5px rgba(0,0,0,0.1);
}

.sidebar h2 {
    text-align: center;
    margin-bottom: 20px;
    font-weight: 600;
}

.chapter {
    padding: 12px 15px;
    margin-bottom: 10px;
    background-color: #374151;
    border-radius: 6px;
    cursor: pointer;
    transition: 0.3s;
    font-weight: 500;
}

.chapter:hover {
    background-color: #4b5563;
    transform: translateX(5px);
}

/* ==============================
   ACTIVITIES SECTION STYLING
============================== */

#title {
    font-size: 26px;
    margin-bottom: 20px;
    color: #1f2937;
    font-weight: 600;
}

#activities {
    list-style: none;
    padding: 0;
    margin: 0;
    max-width: 500px;
}

#activities li {
    margin-bottom: 12px;
}

#activities button {
    width: 100%;
    padding: 12px 15px;
    border: none;
    border-radius: 8px;
    background: linear-gradient(135deg, #1f2937, #1f2937);
    color: white;
    font-size: 15px;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.3s ease;
    text-align: left;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.15);
}

#activities button:hover {
    transform: translateY(-3px);
    box-shadow: 0 8px 15px rgba(0, 0, 0, 0.2);
    background: linear-gradient(135deg, #17294f, #17294f);
}

#activities button:active {
    transform: scale(0.98);
}

.content {
    flex: 1;
    padding: 50px;
}

.content h1 {
    font-size: 32px;
    color: #1f2937;
}

.content p {
    font-size: 18px;
    color: #4b5563;
}

footer {
    text-align: center;
    padding: 15px;
    background: #111827;
    color: white;
}

#exercise2Tools {
    display: none;
}



/* ==============================
   CHAPTER 3 STYLING ONLY
============================== */

.chapter3-box {
    width: 350px;
    margin-top: 20px;
    padding: 20px;
    background: white;
    border-radius: 10px;
    box-shadow: 0 6px 15px rgba(0,0,0,0.1);
}

.chapter3-box h2 {
    text-align: center;
    margin-bottom: 15px;
    color: #1f2937;
}

.chapter3-box label {
    display: block;
    margin-top: 10px;
    font-weight: 500;
    color: #374151;
}

.chapter3-box input {
    width: 100%;
    padding: 8px;
    margin-top: 5px;
    border-radius: 6px;
    border: 1px solid #ccc;
}

.chapter3-box button {
    width: 100%;
    padding: 10px;
    margin-top: 10px;
    border: none;
    border-radius: 6px;
    background-color: #1f2937;
    color: white;
    font-weight: 500;
    cursor: pointer;
    transition: 0.3s;
}

.chapter3-box button:hover {
    background-color: #17294f;
}

.chapter3-box .result {
    margin-top: 15px;
    font-weight: bold;
    color: #111827;
}