I Copied [responsive-columns] Literally and It Didn't Work! Understanding Placeholders vs Real Code

October 29, 2025 · 13 min read

Software Developer

I was following a tutorial and copied this code: <div class="grid [responsive-columns] gap-6"> and NOTHING HAPPENED! 😱 My grid looked broken and I couldn't figure out why. My mentor pointed out the issue immediately: I copied [responsive-columns] literally as a class name! It was a placeholder meant to be replaced with actual Tailwind classes. This embarrassing moment taught me the crucial difference between documentation placeholders and real code. Never again! 🔥

The Code That Did Nothing

Me (Backend Dev): I'm trying to create a responsive grid for my products. I found this example in the docs:

<div className="grid [responsive-columns] gap-6">
  <div>Product 1</div>
  <div>Product 2</div>
  <div>Product 3</div>
</div>

But it's not working! The grid isn't responsive at all. Everything is just stacked vertically. What am I doing wrong?

The Facepalm Moment

Frontend Mentor: laughs Oh no! You've hit the classic "literal placeholder" trap! 😄

Let me show you the problem:

<div className="grid [responsive-columns] gap-6">
                    ↑
                    This is a PLACEHOLDER, not a real class!

What you wrote:

You literally copied [responsive-columns] as a CSS class
Tailwind doesn't understand this! It's not a real class name
It's like telling someone to "go to [your-destination]" and they try to find a place actually called "[your-destination]"

What you should have written:

<div className="grid grid-cols-1 sm:grid-cols-2 md:grid-cols-3 lg:grid-cols-4 gap-6">

Me: OH MY GOD! 🤦‍♂️ I feel so stupid! So [responsive-columns] was just a placeholder that I was supposed to replace?

Frontend Mentor: Don't feel bad! This happens to EVERYONE when they're learning. Let me explain placeholders vs real code!

Understanding Placeholders in Documentation

Frontend Mentor: In documentation and tutorials, you'll often see placeholders that need to be replaced with real values.

Common Placeholder Patterns

Pattern 1: Square Brackets `[placeholder]`

{/* Documentation example */}
<div className="grid [responsive-columns] gap-6">

{/* What you should write */}
<div className="grid grid-cols-1 sm:grid-cols-2 md:grid-cols-3 gap-6">

The rule: Square brackets = placeholder = REPLACE ME!

Pattern 2: Angle Brackets `<placeholder>`

{/* Documentation example */}
<YourComponent name={<user-name>} />

{/* What you should write */}
<YourComponent name="John Doe" />

Pattern 3: ALL_CAPS_PLACEHOLDER

{/* Documentation example */}
const API_KEY = YOUR_API_KEY_HERE;

{/* What you should write */}
const API_KEY = "sk_live_abc123xyz456";

Pattern 4: Ellipsis `...`

{/* Documentation example */}
<div className="grid grid-cols-3 ...">

{/* What you should write */}
<div className="grid grid-cols-3 gap-4 p-4 bg-white">

The ... means: "Add more classes here as needed"

Visual Guide: Spot the Placeholder

Frontend Mentor: Here's how to recognize placeholders:

{/* ❌ PLACEHOLDERS (don't copy literally!) */}
<div className="[your-classes-here]">
<Component prop={<value>} />
<div className="text-[color]">
<div className="w-[size]">
const url = "YOUR_API_URL";

{/* ✅ REAL CODE (copy this!) */}
<div className="grid grid-cols-3 gap-4">
<Component prop="hello" />
<div className="text-blue-500">
<div className="w-64">
const url = "https://api.example.com";

Key insight: If it looks like it's asking you to fill something in, it's a placeholder!

Your Specific Case: Responsive Columns

Me: So what should [responsive-columns] actually be?

Frontend Mentor: Great question! Let me break it down step by step!

What You Had (Broken)

<div className="grid [responsive-columns] gap-6">
  <div>Product 1</div>
  <div>Product 2</div>
  <div>Product 3</div>
  <div>Product 4</div>
</div>

Result:

Product 1
Product 2
Product 3
Product 4

↑ Just a vertical stack! 😢

Why it failed:

[responsive-columns] is NOT a real Tailwind class
Browser ignores unknown classes
Your grid has no column structure
Falls back to default (1 column)

What You Should Have (Working)

<div className="grid grid-cols-1 sm:grid-cols-2 md:grid-cols-3 lg:grid-cols-4 gap-6">
  <div>Product 1</div>
  <div>Product 2</div>
  <div>Product 3</div>
  <div>Product 4</div>
</div>

Result on different screens:

Mobile (< 640px):

[Product 1]
[Product 2]
[Product 3]
[Product 4]

Tablet (640px - 768px):

[Product 1] [Product 2]
[Product 3] [Product 4]

Desktop (768px - 1024px):

[Product 1] [Product 2] [Product 3]
[Product 4]

Large Desktop (> 1024px):

[Product 1] [Product 2] [Product 3] [Product 4]

Breaking Down the Real Classes

Frontend Mentor: Let me explain each part:

<div className="
  grid                  ← Enable CSS Grid
  grid-cols-1           ← 1 column by default (mobile)
  sm:grid-cols-2        ← 2 columns on small screens (≥640px)
  md:grid-cols-3        ← 3 columns on medium screens (≥768px)
  lg:grid-cols-4        ← 4 columns on large screens (≥1024px)
  gap-6                 ← 24px gap between items
">

Each class does something specific:

Class	Breakpoint	Effect
`grid-cols-1`	Default (all)	1 column on mobile
`sm:grid-cols-2`	≥640px	2 columns on tablets
`md:grid-cols-3`	≥768px	3 columns on small laptops
`lg:grid-cols-4`	≥1024px	4 columns on desktops

More Common Placeholder Traps

Me: Are there other placeholders I should watch out for?

Frontend Mentor: Absolutely! Here are the most common ones:

Trap 1: Color Placeholders

{/* ❌ Won't work */}
<div className="bg-[primary-color] text-[secondary-color]">

{/* ✅ Real code */}
<div className="bg-blue-600 text-white">

Trap 2: Size Placeholders

{/* ❌ Won't work */}
<div className="w-[width] h-[height]">

{/* ✅ Real code */}
<div className="w-64 h-48">
{/* or */}
<div className="w-full h-screen">

Trap 3: Spacing Placeholders

{/* ❌ Won't work */}
<div className="p-[padding] m-[margin]">

{/* ✅ Real code */}
<div className="p-4 m-2">

Trap 4: API/URL Placeholders

{/* ❌ Won't work */}
const apiUrl = "YOUR_API_URL";
const apiKey = "YOUR_API_KEY";

{/* ✅ Real code */}
const apiUrl = "https://api.example.com/v1";
const apiKey = "sk_live_abc123xyz789";

Trap 5: Import Placeholders

{/* ❌ Won't work */}
import { YourComponent } from 'your-package';

{/* ✅ Real code */}
import { Button } from '@/components/ui/button';

How to Read Documentation Like a Pro

Me: How do I avoid this in the future?

Frontend Mentor: Here's your guide to reading docs without falling into placeholder traps!

Rule 1: Question Everything in Brackets

When you see brackets, ASK:

Is this a real class name or a placeholder?
Should I replace this with something specific?
Is there an example of the actual value?

Rule 2: Look for Context Clues

Documentation usually provides hints:

{/* Good docs provide examples */}
<div className="grid [responsive-columns] gap-6">
  {/* Example: grid-cols-1 sm:grid-cols-2 md:grid-cols-3 */}
</div>

{/* Or separate sections */}
// Replace [responsive-columns] with:
// - grid-cols-1 sm:grid-cols-2 for two columns
// - grid-cols-1 md:grid-cols-3 for three columns
// - grid-cols-1 sm:grid-cols-2 lg:grid-cols-4 for four columns

Rule 3: Check for "Real World" Examples

Look for complete, working examples:

{/* Placeholder example */}
<Button variant="[variant-name]">Click me</Button>

{/* Real world example */}
<Button variant="primary">Click me</Button>
<Button variant="secondary">Cancel</Button>
<Button variant="destructive">Delete</Button>

Rule 4: Test in Browser DevTools

Quick validation:

Inspect your element
Check the "Computed" tab
If you see [placeholder-name] as a class → IT'S WRONG!
Real Tailwind classes should show computed CSS values

Real vs Placeholder: Side-by-Side

Me: Can you show me more examples side by side?

Frontend Mentor: Absolutely! Here's your cheat sheet:

Grid Layouts

❌ Placeholder	✅ Real Code
`grid [columns]`	`grid grid-cols-3`
`grid [responsive-grid]`	`grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3`
`grid-cols-[number]`	`grid-cols-4`

Colors

❌ Placeholder	✅ Real Code
`bg-[color]`	`bg-blue-500`
`text-[your-color]`	`text-gray-700`
`border-[color-name]`	`border-red-300`

Sizing

❌ Placeholder	✅ Real Code
`w-[width]`	`w-64` or `w-full`
`h-[height]`	`h-48` or `h-screen`
`max-w-[size]`	`max-w-4xl`

Spacing

❌ Placeholder	✅ Real Code
`p-[spacing]`	`p-4`
`m-[margin]`	`m-2`
`gap-[size]`	`gap-6`

Arbitrary Values vs Placeholders

Me: Wait, but I've seen square brackets used for real values! What's the difference?

Frontend Mentor: EXCELLENT question! 🔥 This is where it gets tricky!

Tailwind Arbitrary Values (Real Code!)

These ARE real Tailwind features:

{/* ✅ These work! They're arbitrary values */}
<div className="w-[350px]">          {/* Custom width */}
<div className="bg-[#1da1f2]">       {/* Custom color */}
<div className="top-[117px]">        {/* Custom position */}
<div className="grid-cols-[200px_1fr_1fr]">  {/* Custom grid */}

How to tell the difference:

{/* ❌ PLACEHOLDER (descriptive text) */}
<div className="w-[custom-width]">
                    ↑ Words/description = placeholder

{/* ✅ ARBITRARY VALUE (actual value) */}
<div className="w-[350px]">
                    ↑ Number/color/measurement = real code!

The Decision Tree

See square brackets?
│
├─ Contains actual value (number, color, measurement)?
│  └─ ✅ It's a real arbitrary value! Use it!
│
└─ Contains descriptive text (words, hyphens)?
   └─ ❌ It's a placeholder! Replace it!

Examples Side-by-Side

Syntax	Type	Use It?
`w-[350px]`	Arbitrary value	✅ YES
`bg-[#1da1f2]`	Arbitrary value	✅ YES
`top-[117px]`	Arbitrary value	✅ YES
`w-[custom-width]`	Placeholder	❌ NO, replace it!
`bg-[color]`	Placeholder	❌ NO, replace it!
`[responsive-columns]`	Placeholder	❌ NO, replace it!

Your Complete Responsive Grid

Me: Okay, so what's the COMPLETE, working code for my responsive product grid?

Frontend Mentor: Here's your production-ready code! 🚀

Complete Implementation

{/* Responsive Product Grid */}
<div className="grid grid-cols-1 sm:grid-cols-2 md:grid-cols-3 lg:grid-cols-4 gap-6 p-6">
  {/* Product 1 */}
  <div className="bg-white rounded-lg shadow-md p-4 hover:shadow-lg transition-shadow">
    <img
      src="/product1.jpg"
      alt="Product 1"
      className="w-full h-48 object-cover rounded-md mb-4"
    />
    <h3 className="text-lg font-semibold mb-2">Product 1</h3>
    <p className="text-gray-600 text-sm mb-4">Description here</p>
    <p className="text-xl font-bold text-blue-600">$29.99</p>
  </div>

  {/* Product 2 */}
  <div className="bg-white rounded-lg shadow-md p-4 hover:shadow-lg transition-shadow">
    <img
      src="/product2.jpg"
      alt="Product 2"
      className="w-full h-48 object-cover rounded-md mb-4"
    />
    <h3 className="text-lg font-semibold mb-2">Product 2</h3>
    <p className="text-gray-600 text-sm mb-4">Description here</p>
    <p className="text-xl font-bold text-blue-600">$39.99</p>
  </div>

  {/* Product 3 */}
  <div className="bg-white rounded-lg shadow-md p-4 hover:shadow-lg transition-shadow">
    <img
      src="/product3.jpg"
      alt="Product 3"
      className="w-full h-48 object-cover rounded-md mb-4"
    />
    <h3 className="text-lg font-semibold mb-2">Product 3</h3>
    <p className="text-gray-600 text-sm mb-4">Description here</p>
    <p className="text-xl font-bold text-blue-600">$49.99</p>
  </div>

  {/* Product 4 */}
  <div className="bg-white rounded-lg shadow-md p-4 hover:shadow-lg transition-shadow">
    <img
      src="/product4.jpg"
      alt="Product 4"
      className="w-full h-48 object-cover rounded-md mb-4"
    />
    <h3 className="text-lg font-semibold mb-2">Product 4</h3>
    <p className="text-gray-600 text-sm mb-4">Description here</p>
    <p className="text-xl font-bold text-blue-600">$59.99</p>
  </div>
</div>

What Each Part Does

grid                      ← Enable CSS Grid layout
grid-cols-1               ← Start with 1 column (mobile-first!)
sm:grid-cols-2            ← 2 columns on small screens (tablets)
md:grid-cols-3            ← 3 columns on medium screens (small laptops)
lg:grid-cols-4            ← 4 columns on large screens (desktops)
gap-6                     ← 24px gap between grid items
p-6                       ← 24px padding around the grid

Responsive Grid Variations

Me: Can I customize this for different layouts?

Frontend Mentor: Absolutely! Here are common patterns:

Pattern 1: Two-Column Max (Blog Layout)

<div className="grid grid-cols-1 md:grid-cols-2 gap-6">
  {/* Great for blog posts, articles */}
</div>

Result:

Mobile: 1 column
Desktop: 2 columns

Pattern 2: Three-Column (Most Common)

<div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 gap-6">
  {/* Great for product grids, image galleries */}
</div>

Result:

Mobile: 1 column
Tablet: 2 columns
Desktop: 3 columns

Pattern 3: Four-Column (Dashboard)

<div className="grid grid-cols-1 sm:grid-cols-2 md:grid-cols-3 xl:grid-cols-4 gap-6">
  {/* Great for dashboards, analytics cards */}
</div>

Result:

Mobile: 1 column
Tablet: 2 columns
Laptop: 3 columns
Large desktop: 4 columns

Pattern 4: Auto-Fit (Dynamic)

<div className="grid grid-cols-[repeat(auto-fit,minmax(250px,1fr))] gap-6">
  {/* Automatically fits as many columns as possible */}
</div>

Result:

Automatically adjusts columns based on available space
Each column minimum 250px wide

Debugging Placeholder Issues

Me: How can I catch these mistakes before they waste my time?

Frontend Mentor: Here's your debugging checklist! ✅

Quick Validation Checklist

Step 1: Visual Inspection

{/* 🚩 Red flags to look for */}
className="[anything-with-hyphens]"     ← Suspicious!
className="[descriptive-text]"          ← Placeholder!
className="YOUR_VALUE_HERE"             ← Placeholder!
className="..."                         ← Incomplete!

{/* ✅ Green flags */}
className="grid-cols-3"                 ← Real class!
className="w-[350px]"                   ← Arbitrary value!
className="bg-blue-500"                 ← Real class!

Step 2: Browser DevTools Check

Inspect element
Check "Computed" styles
Look for applied CSS:

❌ If no CSS is applied → Check for placeholder classes!
✅ If CSS is applied → You're good!

Step 3: Tailwind Play Test

Go to https://play.tailwindcss.com/
Paste your code
If it doesn't work there → You have a placeholder or typo!

Common Error Messages

Watch for these clues:

{/* Browser console might show */}
"Unknown class: [responsive-columns]"  ← Placeholder!
"Invalid Tailwind class"               ← Check for placeholders

The Embarrassment Hall of Fame

Me: Am I the only one who's done this?

Frontend Mentor: Not even close! Here are classics everyone has copied literally:

Hall of Fame Entries

{/* Classic #1: The API key */}
const key = "YOUR_API_KEY_HERE";
// Spent 2 hours wondering why API calls failed 😅

{/* Classic #2: The username */}
<p>Welcome, {username}</p>
// Left {username} literally in production 😱

{/* Classic #3: The image path */}
<img src="/path/to/your/image.jpg" />
// Literally created a folder called "path/to/your" 🤦‍♂️

{/* Classic #4: The color */}
<div className="bg-[your-color-here]">
// "Why is my background transparent??" 😂

{/* Classic #5: The TODO */}
// TODO: Add error handling
// Left in production for 6 months 💀

You're in good company! 🎉

Key Takeaways

Me: Let me make sure I've got this!

Frontend Mentor: Perfect! Here's your cheat sheet:

The Golden Rules

Square brackets with descriptive text = PLACEHOLDER
- [responsive-columns] ❌
- [your-color] ❌
- [custom-size] ❌
Square brackets with actual values = REAL CODE
- [350px] ✅
- [#1da1f2] ✅
- [200px_1fr_1fr] ✅
When in doubt, ask:
- Is this a description or a value?
- Would this make sense to a computer?
- Is there an example nearby?

Your Responsive Grid Formula

{/* ❌ WRONG (placeholder) */}
<div className="grid [responsive-columns] gap-6">

{/* ✅ RIGHT (real code) */}
<div className="grid grid-cols-1 sm:grid-cols-2 md:grid-cols-3 lg:grid-cols-4 gap-6">

Quick Reference Card

Pattern	Type	Action
`[descriptive-text]`	Placeholder	Replace it!
`[123px]`	Arbitrary value	Use it!
`[#abc123]`	Arbitrary value	Use it!
`YOUR_VALUE`	Placeholder	Replace it!
`...`	Incomplete	Add more!

The Ultimate Test

Before you use any class, ask:

"If I showed this to a computer, would it understand what to do?"

❌ [responsive-columns] → Computer confused!
✅ grid-cols-3 → Computer knows exactly what to do!

Me: I'll never copy [responsive-columns] literally again! This was embarrassing but I learned SO much. Now I know how to spot placeholders and what the actual responsive grid classes should be!

Frontend Mentor: That's the spirit! 🚀 Making mistakes is how we learn! You've just leveled up from "blindly copying code" to "understanding what each part means." Next time you see square brackets with descriptive text, you'll know: "Aha! That's a placeholder—I need to replace it with real values!"

Now go build that awesome responsive product grid! 💪

Have you ever copied a placeholder literally? Share your funniest coding mistakes in the comments! 😄💬

The Code That Did Nothing​

The Facepalm Moment​

Understanding Placeholders in Documentation​

Common Placeholder Patterns​

Pattern 1: Square Brackets [placeholder]​

Pattern 2: Angle Brackets <placeholder>​

Pattern 3: ALL_CAPS_PLACEHOLDER​

Pattern 4: Ellipsis ...​

Visual Guide: Spot the Placeholder​

Your Specific Case: Responsive Columns​

What You Had (Broken)​

What You Should Have (Working)​

Breaking Down the Real Classes​

More Common Placeholder Traps​

Trap 1: Color Placeholders​

Trap 2: Size Placeholders​

Trap 3: Spacing Placeholders​

Trap 4: API/URL Placeholders​

Trap 5: Import Placeholders​

How to Read Documentation Like a Pro​

Rule 1: Question Everything in Brackets​

Rule 2: Look for Context Clues​

Rule 3: Check for "Real World" Examples​

Rule 4: Test in Browser DevTools​

Real vs Placeholder: Side-by-Side​

Grid Layouts​

Colors​

Sizing​

Spacing​

Arbitrary Values vs Placeholders​

Tailwind Arbitrary Values (Real Code!)​

The Decision Tree​

Examples Side-by-Side​

Your Complete Responsive Grid​

Complete Implementation​

What Each Part Does​

Responsive Grid Variations​

Pattern 1: Two-Column Max (Blog Layout)​

Pattern 2: Three-Column (Most Common)​

Pattern 3: Four-Column (Dashboard)​

Pattern 4: Auto-Fit (Dynamic)​

Debugging Placeholder Issues​

Quick Validation Checklist​

Step 1: Visual Inspection​

Step 2: Browser DevTools Check​

Step 3: Tailwind Play Test​

Common Error Messages​

The Embarrassment Hall of Fame​

Hall of Fame Entries​

Key Takeaways​

The Golden Rules​

Your Responsive Grid Formula​

Quick Reference Card​

The Ultimate Test​

The Code That Did Nothing

The Facepalm Moment

Understanding Placeholders in Documentation

Common Placeholder Patterns

Pattern 1: Square Brackets `[placeholder]`

Pattern 2: Angle Brackets `<placeholder>`

Pattern 3: ALL_CAPS_PLACEHOLDER

Pattern 4: Ellipsis `...`

Visual Guide: Spot the Placeholder

Your Specific Case: Responsive Columns

What You Had (Broken)

What You Should Have (Working)

Breaking Down the Real Classes

More Common Placeholder Traps

Trap 1: Color Placeholders

Trap 2: Size Placeholders

Trap 3: Spacing Placeholders

Trap 4: API/URL Placeholders

Trap 5: Import Placeholders

How to Read Documentation Like a Pro

Rule 1: Question Everything in Brackets

Rule 2: Look for Context Clues

Rule 3: Check for "Real World" Examples

Rule 4: Test in Browser DevTools

Real vs Placeholder: Side-by-Side

Grid Layouts

Colors

Sizing

Spacing

Arbitrary Values vs Placeholders

Tailwind Arbitrary Values (Real Code!)

The Decision Tree

Examples Side-by-Side

Your Complete Responsive Grid

Complete Implementation

What Each Part Does

Responsive Grid Variations

Pattern 1: Two-Column Max (Blog Layout)

Pattern 2: Three-Column (Most Common)

Pattern 3: Four-Column (Dashboard)

Pattern 4: Auto-Fit (Dynamic)

Debugging Placeholder Issues

Quick Validation Checklist

Step 1: Visual Inspection

Step 2: Browser DevTools Check

Step 3: Tailwind Play Test

Common Error Messages

The Embarrassment Hall of Fame

Hall of Fame Entries

Key Takeaways

The Golden Rules

Your Responsive Grid Formula

Quick Reference Card

The Ultimate Test