Square bracket notation for custom values in Tailwind - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is square bracket notation in Tailwind CSS?

Square bracket notation lets you use custom CSS values directly in Tailwind classes, like bg-[#ff6347] for a custom background color.

beginner

How do you write a custom width of 37 pixels using square bracket notation?

You write it as w-[37px]. This tells Tailwind to apply a width of exactly 37 pixels.

intermediate

Can you use square bracket notation for any CSS property in Tailwind?

Yes, as long as Tailwind supports that property, you can use square brackets to add any valid CSS value, like text-[1.25rem] or mt-[10vh].

beginner

Why is square bracket notation useful in Tailwind CSS?

It lets you quickly add unique styles without editing config files or writing extra CSS, keeping your code simple and fast.

beginner

Example: What does text-[20px] do in Tailwind?

It sets the font size to exactly 20 pixels, overriding default sizes.

How do you set a custom background color #123abc using Tailwind's square bracket notation?

A bg-#123abc

B bg{123abc}

C bg(123abc)

D bg-[#123abc]

Square bracket notation requires brackets around the value, so bg-[#123abc] is correct.

Which of these is a valid Tailwind class for a custom margin of 15 pixels?

A m-[15px]

B margin-15px

C m-15

D m(15px)

Tailwind uses square brackets for custom values, so m-[15px] is valid.

Can you use square bracket notation to set a custom font size of 2rem?

A Yes, use <code>text-[2rem]</code>.

B No, Tailwind only allows predefined sizes.

C Yes, but only in the config file.

D No, you must write custom CSS.

Square bracket notation lets you set any valid CSS value inline, like text-[2rem].

What happens if you write w-[50] without units in Tailwind?

A It sets width to 50 percent.

B It sets width to 50 pixels.

C It causes an error or is ignored.

D It sets width to 50 em.

CSS values need units; without units like px or %, Tailwind ignores or errors on the value.

Which Tailwind class sets a custom padding of 3.5rem using square bracket notation?

A padding-3.5rem

B p-[3.5rem]

C p-3.5

D p(3.5rem)

Square bracket notation with units is p-[3.5rem].

Explain how square bracket notation works in Tailwind CSS and why it is helpful.

Think about how you add unique styles without extra CSS files.

Give three examples of Tailwind classes using square bracket notation for different CSS properties.

Use brackets with values like colors, px, rem units.

Practice

1. What does the square bracket notation in Tailwind CSS allow you to do?

easy

A. Disable Tailwind's default styles

B. Write JavaScript code inside Tailwind classes

C. Create new Tailwind utility classes permanently

D. Use custom CSS values not included in Tailwind's default set

Solution

1. Step 1: Understand Tailwind's default values

   Tailwind provides a set of predefined values for spacing, colors, sizes, etc.

2. Step 2: Role of square bracket notation

   Square bracket notation lets you write any CSS value directly inside a class, like mt-[10px] for margin-top 10 pixels.

3. Final Answer:

   Use custom CSS values not included in Tailwind's default set -> Option D

4. Quick Check:

   Square brackets = custom CSS values [OK]

Hint: Square brackets mean custom CSS values inside Tailwind classes [OK]

Common Mistakes:

• Thinking it creates new permanent classes
• Confusing with JavaScript code inside classes
• Assuming it disables Tailwind styles

2. Which of the following is the correct Tailwind class to set a width of exactly 250 pixels using square bracket notation?

easy

A. width-[250]

B. w-[250px]

C. w-250px

D. w-[250]

Solution

1. Step 1: Identify correct Tailwind prefix for width

   Tailwind uses w- prefix for width utilities.

2. Step 2: Use square brackets with full CSS value

   Inside brackets, you must include the unit, so 250px is correct.

3. Final Answer:

   w-[250px] -> Option B

4. Quick Check:

   Width with unit inside brackets = w-[250px] [OK]

Hint: Use full CSS value with units inside brackets after utility prefix [OK]

Common Mistakes:

• Omitting units inside brackets
• Using wrong prefix like width-
• Not using brackets for custom values

3. What will be the rendered width of a div with class class="w-[15rem]" in Tailwind CSS?

medium

A. 15 rem units (usually 15 times root font size)

B. 15 pixels

C. 15 percent width

D. 15 viewport width units

Solution

1. Step 1: Understand the CSS unit inside brackets

   The class w-[15rem] sets width to 15 rem units, where 1 rem equals the root font size (usually 16px).

2. Step 2: Interpret the rendered size

   15 rem means 15 times the root font size, so it is not pixels or percent but relative to font size.

3. Final Answer:

   15 rem units (usually 15 times root font size) -> Option A

4. Quick Check:

   Square bracket value with rem = relative font size width [OK]

Hint: Read units inside brackets literally as CSS units [OK]

Common Mistakes:

• Assuming rem means pixels
• Confusing rem with percent or viewport units
• Ignoring units inside brackets

4. You wrote class="p-[20]" to add padding of 20 pixels, but it doesn't work. What is the error?

medium

A. Padding cannot be customized in Tailwind

B. Square brackets are not allowed for padding

C. Missing unit inside square brackets

D. Class name should be padding-[20px]

Solution

1. Step 1: Check the syntax of the custom value

   Inside square brackets, you must include the CSS unit, like 20px, not just a number.

2. Step 2: Understand Tailwind's requirement for units

   Without units, the CSS value is invalid, so the style won't apply.

3. Final Answer:

   Missing unit inside square brackets -> Option C

4. Quick Check:

   Always include units inside brackets for custom values [OK]

Hint: Always add units like px, rem inside brackets for spacing [OK]

Common Mistakes:

• Omitting units inside brackets
• Using wrong class names like padding-
• Thinking padding can't be customized

5. You want a button with a background color exactly #1a73e8 and a border radius of 12px using Tailwind's square bracket notation. Which class combination is correct?

hard

A. bg-[#1a73e8] rounded-[12px]

B. bg-#1a73e8 rounded-12px

C. background-[#1a73e8] border-radius-[12px]

D. bg-[#1a73e8] rounded-[12]

Solution

1. Step 1: Use correct Tailwind prefixes

   Background color uses bg- and border radius uses rounded-.

2. Step 2: Apply square bracket notation with full CSS values

   Inside brackets, include the full hex color #1a73e8 and the unit 12px for radius.

3. Step 3: Check for syntax correctness

   bg-[#1a73e8] rounded-[12px] uses correct prefixes and proper bracket notation with units and hash symbol.

4. Final Answer:

   bg-[#1a73e8] rounded-[12px] -> Option A

5. Quick Check:

   Use correct prefixes + full CSS values in brackets [OK]

Hint: Use bg- and rounded- with full CSS values inside brackets [OK]

Common Mistakes:

• Omitting # in hex color
• Missing units for border radius
• Using wrong prefixes like background-