The CSS does not work as needed. To see the entire viewing area, I have to set my browser at 80%. I need a complete replacement that looks at the screen resolution and sets the viewing panel to the browser width. The Image panel needs to be 75% of the viewing panel width and the text panel to 25%. We need a scroll bar on the text panel.

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

html, body {
    margin: 0;
    padding: 0;
    height: 100%;
    width: 100%;
    box-sizing: border-box;
    overflow: hidden;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
}

.container {
    display: flex;
    flex-direction: column;
    height: 100vh;
    width: 100vw;
}

.header {
    flex: 0 0 auto;
    padding: 10px;
    text-align: center;
    background: rgba(255, 255, 255, 0.8);
}

.header h1 {
    color: #333;
    font-size: 2em;
    font-weight: 300;
    text-shadow: 0 1px 2px rgba(0, 0, 0, 0.1);
}

.content {
    flex: 1 1 auto;
    display: flex;
    overflow: hidden;
}

.panel {
    height: 100%;
    display: flex;
    flex-direction: column;
    padding: 10px;
    overflow: hidden;
}

.panel:nth-child(1) {
    width: 75%;
}

.panel:nth-child(2) {
    width: 25%;
}

.panel h2 {
    color: #444;
    margin-bottom: 5px;
    font-size: 1.5em;
    font-weight: 400;
    text-align: center;
    border-bottom: 1px solid #f0f0f0;
    padding-bottom: 5px;
}

.image-container {
    flex: 1;
    background: #f8f9fa;
    display: flex;
    justify-content: center;
    align-items: center;
    border: 1px dashed #ddd;
    overflow: auto;
}

.image-container.has-image {
    background: transparent;
    border: none;
}

.image-container img {
    max-width: 100%;
    max-height: 100%;
    border-radius: 5px;
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1);
}

.placeholder {
    color: #999;
    font-size: 1em;
    text-align: center;
}

.text-container {
    flex: 1;
    background: #f8f9fa;
    border: 1px solid #e9ecef;
    border-radius: 5px;
    padding: 10px;
    overflow-y: auto;
}

.text-container::-webkit-scrollbar {
    width: 8px;
}

.text-container::-webkit-scrollbar-track {
    background: #e9ecef;
    border-radius: 4px;
}

.text-container::-webkit-scrollbar-thumb {
    background: #667eea;
    border-radius: 4px;
}

.text-container::-webkit-scrollbar-thumb:hover {
    background: #764ba2;
}

.text-content {
    color: #333;
    line-height: 1.5;
    font-size: 1em;
    white-space: pre-wrap;
    word-wrap: break-word;
}

.controls {
    flex: 0 0 auto;
    padding: 10px;
    background: rgba(255, 255, 255, 0.7);
    display: flex;
    justify-content: space-around;
    align-items: center;
    gap: 10px;
}

.page-input {
    display: flex;
    align-items: center;
    gap: 5px;
    font-size: 1em;
    color: #444;
}

.page-input input {
    width: 60px;
    padding: 5px;
    border: 1px solid #ddd;
    border-radius: 5px;
    text-align: center;
    font-size: 1em;
    transition: border-color 0.2s ease;
}

.page-input input:focus {
    outline: none;
    border-color: #667eea;
    box-shadow: 0 0 0 2px rgba(102, 126, 234, 0.1);
}

.nav-btn {
    background: linear-gradient(135deg, #667eea, #764ba2);
    color: white;
    border: none;
    padding: 5px 10px;
    border-radius: 5px;
    cursor: pointer;
    font-size: 1em;
    transition: all 0.2s ease;
    box-shadow: 0 2px 5px rgba(102, 126, 234, 0.2);
}

.nav-btn:hover {
    transform: translateY(-1px);
    box-shadow: 0 3px 7px rgba(102, 126, 234, 0.3);
}

.nav-btn:active {
    transform: translateY(0);
}

.nav-btn:disabled {
    background: #ccc;
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
}

.error {
    color: #e74c3c;
    text-align: center;
    font-style: italic;
}

@media (max-width: 768px) {
    .content {
        flex-direction: column;
    }

    .panel {
        width: 100%;
        min-height: 50vh;
    }

    .panel:nth-child(1) { /* Image panel */
        width: 100%;
    }

    .panel:nth-child(2) { /* Text panel */
        width: 100%;
    }

    .header h1 {
        font-size: 1.5em;
    }

    .controls {
        flex-wrap: wrap;
        justify-content: center;
    }
}

@media (min-width: 769px) {
    .content {
        flex-direction: row;
    }

    .panel:nth-child(1) { /* Image panel */
        width: 75%;
    }

    .panel:nth-child(2) { /* Text panel */
        width: 25%;
    }
}

@media (max-height: 600px) {
    .header h1 {
        font-size: 1.2em;
    }

    .panel h2 {
        font-size: 1.2em;
    }

    .text-content {
        font-size: 0.9em;
    }

    .controls {
        padding: 5px;
    }

    .nav-btn, .page-input input {
        font-size: 0.9em;
        padding: 4px 8px;
    }
}

Here is the HTML:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Image & Text Viewer</title>
    <link rel="stylesheet" href="styles.css">
</head>
<body>
    <div class="container">
        <div class="header">
            <h1>Image & Text Viewer</h1>
        </div>
        
        <div class="content">
            <div class="panel">
                <h2>Image</h2>
                <div class="image-container" id="imageContainer">
                    <div class="placeholder">No image loaded</div>
                </div>
            </div>
            
            <div class="panel">
                <h2>Text</h2>
                <div class="text-container" id="textContainer">
                    <div class="text-content" id="textContent">
                        <div class="placeholder">No text loaded</div>
                    </div>
                </div>
            </div>
        </div>
        
        <div class="controls">
            <button class="nav-btn" id="prevBtn">◀ Previous</button>
            
            <div class="page-input">
                <label for="pageNumber">Page</label>
                <input type="number" id="pageNumber" value="1" min="1">
            </div>
            
            <button class="nav-btn" id="nextBtn">Next ▶</button>
            
            <button class="nav-btn" id="refreshBtn">🔄 Refresh</button>
        </div>
    </div>

    <script src="script.js"></script>
</body>
</html>