Background color in CSS - Practice Problems & Coding Challenges

Challenge - 5 Problems

📝 Syntax

intermediate

What is the background color of this box?

Look at the CSS code below. What color will the box show as its background?

CSS

div {
  background-color: #ff6347;
  width: 100px;
  height: 100px;
}

A A shade of orange-red (tomato color)

B A bright red color

C A dark blue color

D A light green color

💡 Hint

The hex code #ff6347 is known as tomato color.

The hex code #ff6347 corresponds to a tomato color, which is a shade of orange-red. It is not pure red or blue or green.

❓ rendering

intermediate

Which background color will fill the entire viewport?

Given this CSS, what color will fill the entire browser window background?

CSS

body {
  background-color: rgb(0, 128, 0);
  margin: 0;
  height: 100vh;
}

A A medium green color filling the whole window

B No background color visible because height is zero

C A transparent background showing default white

D A blue background filling the window

💡 Hint

The rgb(0, 128, 0) is a green color. The height 100vh means full viewport height.

The background-color is set to rgb(0, 128, 0), which is a medium green. The height: 100vh makes the body fill the full viewport height, and margin: 0 removes default spacing, so the green fills the entire window.

❓ selector

advanced

Which CSS selector changes background color only for paragraphs inside a section?

You want to change the background color of only <p> tags inside <section> elements. Which selector does this correctly?

A p > section { background-color: lightblue; }

B p section { background-color: lightblue; }

C section > p { background-color: lightblue; }

D section p { background-color: lightblue; }

💡 Hint

Think about the order: parent then child in selectors.

The selector section p targets all <p> elements inside any <section>. Option D selects only direct children, which is more restrictive but still valid. However, option D is the general correct selector for paragraphs inside sections.

❓ accessibility

advanced

Why should you avoid pure black background with pure white text?

What is a main accessibility concern when using pure black (#000000) background with pure white (#FFFFFF) text?

A It disables screen readers

B It breaks keyboard navigation

C It causes eye strain due to very high contrast

D It is not readable on mobile devices

💡 Hint

Think about how your eyes feel reading very bright text on dark background.

Pure black and pure white create very high contrast which can cause eye strain for many users. Accessibility guidelines recommend softer contrasts for better readability and comfort.

🧠 Conceptual

expert

What happens if you set background-color with alpha transparency on a semi-transparent element?

Consider this CSS: .box { background-color: rgba(255, 0, 0, 0.5); opacity: 0.5; width: 100px; height: 100px; } What will be the visual effect on the box's background color?

A The box background will be fully opaque red ignoring opacity

B The box background will be very faint red because opacity multiplies transparency

C The box background will be solid red with no transparency

D The box background will be invisible

💡 Hint

Opacity affects the whole element including background color transparency.

The background-color has 50% transparency (alpha 0.5). The opacity: 0.5 applies to the entire element, making it 50% transparent as well. These transparencies multiply, so the visible background is even more faint red.