safe-css-append

name	safe-css-append
description	Safely append CSS styles from one file to another by identifying missing rules, adapting CSS variables, and verifying changes

Safe CSS Append Workflow

This skill provides a systematic approach for safely appending CSS styles from a source file to a destination file. The workflow ensures no content is overwritten, CSS variables are properly adapted, and all changes are verified.

When to Use This Skill

• Migrating styles between projects
• Copying component styles while preserving existing rules
• Adding new CSS rules without duplicating or conflicting with existing styles
• Adapting styles to use a different set of CSS variables

Workflow Steps

1. Read and Analyze Source CSS

First, examine the source CSS file to identify the selectors and rules you want to transfer:

# Read the source CSS file
cat /path/to/source/styles.css

# Identify specific selectors if needed
grep "selector-pattern" /path/to/source/styles.css

Document:

• Target selectors (e.g., .panel-tab, .header-nav)
• CSS variables used (e.g., --primary-color, --spacing-unit)
• Complete rule sets for each selector

2. Read and Check Destination CSS

Examine the destination file to understand existing rules and avoid duplication:

# Read the destination CSS file
cat /path/to/destination/styles.css

# Check if specific selectors already exist
grep "selector-name" /path/to/destination/styles.css

# Check for existing CSS variables
grep "^[[:space:]]*--" /path/to/destination/styles.css | head -20

Identify:

• Existing selectors that might conflict
• CSS variable naming conventions in the destination
• Any existing rules for the target selectors

3. Identify Missing Styles and Required Adaptations

Compare source and destination to determine:

• Which selectors are completely missing
• Which properties are missing from existing selectors
• How CSS variables need to be mapped (source → destination)

Example variable mapping:

Source: --panel-bg → Destination: --background-secondary
Source: --text-primary → Destination: --color-text-primary
Source: --border-radius → Keep as-is (if already defined in destination)

4. Prepare Adapted CSS Content

Create the CSS content to append, adapting variables as needed:

/* Example adapted CSS */
.new-selector {
    background-color: var(--background-secondary);  /* was --panel-bg */
    color: var(--color-text-primary);               /* was --text-primary */
    border-radius: var(--border-radius);            /* unchanged */
    padding: 8px 16px;
}

.existing-selector {
    /* Only add missing properties, not the entire rule */
    new-property: value;
}

5. Safely Append to Destination

Use append operations (never overwrite) to add the new styles:

# Append new CSS rules
cat >> /path/to/destination/styles.css << 'EOF'

/* Added styles from source project */
.selector-name {
    property: value;
    variable-property: var(--adapted-variable);
}
EOF

Best practices:

• Add a comment indicating the source or purpose
• Include a blank line before the new content for readability
• Use >> (append) never > (overwrite)

6. Verify the Changes

Confirm that the styles were added correctly:

# View the last N lines to see appended content
tail -n 20 /path/to/destination/styles.css

# Verify specific selectors were added
grep "new-selector-name" /path/to/destination/styles.css

# Check the complete file if needed
cat /path/to/destination/styles.css | tail -n 50

Complete Example

Here's a full example workflow:

# 1. Read source CSS and identify target
cat project-a/components.css | grep -A 10 ".button-primary"

# 2. Check destination for conflicts
grep ".button-primary" project-b/main.css
grep "^[[:space:]]*--btn-" project-b/main.css

# 3. Identify that .button-primary is missing, and variables need mapping:
#    --btn-color → --primary-color (exists in destination)
#    --btn-padding → create inline value

# 4. Append adapted styles
cat >> project-b/main.css << 'EOF'

/* Button styles from project-a */
.button-primary {
    background-color: var(--primary-color);
    padding: 10px 20px;
    border-radius: 4px;
    font-weight: 600;
}
EOF

# 5. Verify
tail -n 10 project-b/main.css
grep ".button-primary" project-b/main.css

Safety Checklist

• Source file read and analyzed
• Destination file checked for existing rules
• Missing styles identified
• CSS variables mapped correctly
• Append operation used (not overwrite)
• Changes verified with tail/grep
• No duplicate selectors created
• All variable references exist in destination

Common Pitfalls

1. Overwriting instead of appending: Always use >>, never >
2. Variable mismatch: Ensure all CSS variables exist in the destination or are properly defined
3. Duplicate selectors: Check for existing rules before adding complete selector blocks
4. Missing verification: Always verify changes after appending

Tips

• Use wc -l before and after to confirm lines were added
• Keep a mapping document for complex variable transformations
• Consider using a temporary file to preview changes before appending
• Group related selectors together when appending multiple rules