Common HTML mistakes - Practice Problems & Coding Challenges

Challenge - 5 Problems

📝 Syntax

intermediate

What error does this HTML snippet cause?

Look at this HTML code:

<div>Hello<span>World</div></span>

What problem will this cause when rendered in a browser?

HTML

<div>Hello<span>World</span></div>

A The browser will close the <span> before the </div>, causing incorrect nesting.

B The browser will render correctly with no visible issues.

C The browser will throw a syntax error and stop rendering the page.

D The browser will ignore the <span> tag completely.

💡 Hint

Think about how tags must open and close in the right order.

HTML tags must be properly nested. Here, <span> is opened inside <div> but closed after </div>, which breaks nesting. Browsers fix this by closing <span> early, changing the structure.

❓ accessibility

intermediate

Which option improves accessibility for this image?

You have this image tag:

<img src="flower.jpg">

Which option adds the best accessibility improvement?

HTML

<img src="flower.jpg">

A <img src="flower.jpg" role="presentation">

B <img src="flower.jpg" title="flower">

C <img src="flower.jpg" aria-hidden="true">

D <img src="flower.jpg" alt="A red flower in a garden">

💡 Hint

Think about screen readers and what they need to describe images.

The alt attribute provides descriptive text for screen readers, helping visually impaired users understand the image content. Title is less reliable, aria-hidden hides the image from assistive tech, and role="presentation" removes semantic meaning.

❓ layout

advanced

What visual issue occurs with this CSS and HTML?

Given this HTML and CSS:

<div class="container"><div class="box">Box</div></div>

.container { display: flex; } .box { width: 100px; margin-left: auto; }

What will happen to the box inside the container?

HTML

<div class="container"><div class="box">Box</div></div>

A The box will be aligned to the left side ignoring margin-left.

B The box will be centered horizontally inside the container.

C The box will be aligned to the right side of the container.

D The box will overflow outside the container.

💡 Hint

Remember how margin auto works inside flex containers.

In a flex container, margin-left: auto pushes the item to the right, aligning it at the container's end.

❓ selector

advanced

Which CSS selector matches only direct children?

You want to style only <li> elements that are direct children of <ul>.
Which selector should you use?

A ul li

B ul > li

C ul + li

D ul ~ li

💡 Hint

Think about the difference between descendant and child selectors.

The '>' selector matches only direct children. 'ul li' matches all descendants, including nested ones. '+' and '~' select siblings, not children.

🧠 Conceptual

expert

What is the effect of missing viewport meta tag on mobile?

Consider a webpage without this tag:

<meta name="viewport" content="width=device-width, initial-scale=1">

What will happen when viewed on a mobile device?

A The page will zoom out and show a desktop-sized layout, making text small and hard to read.

B The page will automatically switch to a mobile-friendly layout.

C The page will not load at all on mobile devices.

D The page will scale to fit the device width and look good on mobile.

💡 Hint

Think about how browsers handle page scaling without instructions.

Without the viewport meta tag, mobile browsers assume a desktop width and zoom out, causing small text and poor usability.