:root {
    --primary: #0561ff;
    --success: #218838;
    --bg: #f4f7f6;
    --text: #333;
}

body {
    font-family: 'Segoe UI', system-ui, sans-serif;
    background-color: var(--bg);
    margin: 0; padding: 0;
    color: var(--text);
}

.main-nav {
    background: #fff;
    box-shadow: 0 2px 10px rgba(0,0,0,0.05);
    padding: 15px 0;
    position: sticky; top: 0; z-index: 100;
}

.nav-container {
    max-width: 900px;
    margin: 0 auto;
    display: flex;
    justify-content: center;
    gap: 15px;
    flex-wrap: wrap;
}

.nav-item {
    text-decoration: none;
    color: #555;
    font-weight: 600;
    padding: 8px 16px;
    border-radius: 20px;
    transition: 0.3s;
    font-size: 0.9rem;
}

.nav-item:hover { background: #f0f7ff; color: var(--primary); }
.nav-item.active { background: var(--primary); color: #fff; }

.container {
    background: #fff;
    max-width: 700px;
    margin: 30px auto;
    padding: 25px;
    border-radius: 15px;
    box-shadow: 0 10px 25px rgba(0,0,0,0.05);
}

header { text-align: center; margin-bottom: 25px; }
.upload-section { margin-bottom: 20px; }
input[type="file"] { display: none; }
.custom-file-upload {
    display: block; border: 2px dashed var(--primary);
    padding: 30px; text-align: center;
    border-radius: 10px; cursor: pointer;
    background: #f0f7ff; color: var(--primary);
}

.preview-box {
    margin: 20px 0; border: 1px solid #eee;
    padding: 15px; border-radius: 8px; text-align: center;
}
.preview-box img, .preview-box canvas { max-width: 100%; border-radius: 5px; }

.settings-section { background: #fafafa; padding: 20px; border-radius: 10px; border: 1px solid #eee; }
.form-group { margin-bottom: 15px; }
label { display: block; margin-bottom: 8px; font-weight: 600; }
select, input[type="text"], input[type="number"], textarea {
    width: 100%; padding: 10px; border: 1px solid #ddd; border-radius: 5px; box-sizing: border-box;
}

.btn-primary { 
    width: 100%; padding: 12px; background: var(--primary);
    color: #fff; border: none; border-radius: 5px;
    font-weight: bold; cursor: pointer;
}
.btn-success {
    display: block; width: 100%; padding: 12px;
    background: var(--success); color: #fff;
    text-decoration: none; border-radius: 5px;
    font-weight: bold; margin-top: 15px; text-align: center;
}

.hidden { display: none; }

/* ... Giữ nguyên phần cũ ... */
footer {
    text-align: center;
    padding: 30px 0;
    color: #888;
    font-size: 0.85rem;
}