In an interview, sometimes the basic questions are hard to answer. I have faced the same situation. It's always better to assemble important questions so that you can avoid browsing the web, and searching for answers when you have less time. Therefore, I have combined some CSS questions which I have faced in various interviews. I hope, you find it useful.

Q1

✍Why CSS is important?

• CSS controls all design related aspects of a web page. Without CSS, the webpage is only a skeleton with plain texts, images, etc.
• By CSS, we add typography, styles and layouts. It makes our webpage look pretty.

Q2

✍What do you mean by meta tag? And why initial value =1.0 written?

• The <meta> tag defines metadata about an HTML document. Metadata is data (information) about data.
• <meta> tags always go inside the element, and are typically used to specify character set, page description, keywords, author of the document, and viewport settings.It is machine parsable.
• Metadata is used by browsers (how to display content or reload page), search engines (keywords), and other web services.

Q3

✍Units in CSS. Difference between absolute, relative, and fixed.

There are 4 types of layouts.

• position: static: HTML elements are positioned static by default. top, left, right and bottom properties won’t have any effect.
• position: relative: places an element relative to its current position without changing the layout around it.
• position: absolute: places an element relative to its parent’s position and changing the layout around it.
• position: fixed: It is positioned relative to the viewport, which means it always stays in the same place even if the page is scrolled.

Q4

✍Explain CSS pseudo-selectors, pseudo-classes and pseudo-elements.

• Pseudo Selectors are given to add some special features to elements, like content::before, content::after, p::first-letter etc.
• A CSS pseudo-class is a keyword preceded by a colon (:) that is added on to the end of selectors to specify that you want to style the selected elements only when they are in certain state. e.g. :active, :hover, :focus, :visited
• Pseudo-elements are very much like pseudo-classes, but they have differences. They are keywords — this time preceded by two colons (::) — that can be added to the end of selectors to select a certain part of an element.

Q5

✍What are media queries and explain them in detail.

• Media query is a CSS technique introduced in CSS3. It uses the @media rule to include a block of CSS properties only if a certain condition is true.

  @media only screen and (max-width: 600px) {
  body {
    background-color: lightblue;
  }
  }
  

Q6

✍Explain box-model.

All the HTML elements can be considered boxes. The box model wraps every HTML element. A Box model consists of margins, borders, padding, and the actual content.

Q7

✍Difference between transition and transform property in CSS.

• The Transform property in CSS moves or modifies the appearance of an element, whereas the Transition property seamlessly and gently transitions the element from one state to another.

  #box4{
    width: 120px;
    height: 120px;
    background-color: red;
    border-radius: 12px;
    transition: all 0.7s ease;
  }
  #box4:hover{ transform: rotate(25deg); }
  

Q8

✍What is Mobile-First Approach and Desktop First approach and which one you follow and why?

• The term Mobile-First means that when developing a website, we start writing the CSS for smaller viewport sizes first, and then use CSS media queries to alter the experience for larger ones (e.g: tablets or desktops). For Desktop First, it's the other way around.
• It is easier to simplify a Desktop First Design. But it depends on the requirements of the website whether and the user base.

Q9

✍Write a piece of code to center div.

// method 1
.parent-div {
    position: relative;
}
.child-div {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

// method 2: using flex
.parent-div {
    display: flex;
    height: 100vh;
}
.child-div {
    justify-content: center;
    align-items: center;
}

Q10

✍How we can achieve smooth scrolling?

<nav>
    <ul>
        <li><a href="#first-section">First Section</a></li>
        <li><a href="#second-section">Second Section</a></li>
        <li><a href="#third-section">Third Section</a></li>
    </ul>
</nav>

<section id="first-section"></section>
<section id="second-section"></section>
<section id="third-section"></section>

<style>
html {
    scroll-behavior: smooth;
}
</style>

Q11

✍What is specificity in CSS? Explain in detail.

• Specificity is a set of rules which browser follows to decide when encountered with ambiguous CSS styles.
• For example, if 2 divs are same styles, then the style of below div will always work.
• id will get preference over class.
• !important will get most preference, above id or class.

Q12

✍What is a responsive web design and adaptive web design.

• The responsive design will reconfigure all design elements whether it's viewed on a desktop, laptop, tablet, or mobile phone.
• With adaptive design, different fixed layouts are created that adapt to the users screen size.
• Adaptive design is faster to load.

Q13

✍What is flexbox and explain their properties.

• Flexbox Layout Model was designed as a one-dimensional layout model.
• It makes it easier to design flexible responsive layout structure without using float or positioning.
• Some of the properties are
  • justify-content
  • align-items
  • flex-basis
  • flex-direction
  • flex-wrap
  • flex-grow
  • order

Q14

✍Difference between justify-content vs align-items.

• justify-content — controls alignment of all items on the main axis (horizontal).
• align-items — controls alignment of all items on the cross axis (vertical).

Q15

✍Difference between id and class selectors.

• Class can be reused. IDs are unique.
• Classes are represented by (.) where IDs by (#).
• Normally ID take more preference than class. See specificity.

Q16

✍How will you decide when to use a button or tag?

• Generally, I use <a> for links and navigation between page / views.
• I use <button> for actions, for example on the current page : validating/resetting a form, showing a modal, etc.

Q17

✍What are some of the things you would test while doing accessibility testing?

• Accessibility Testing is defined as a type of Software Testing performed to ensure that the application being tested is usable by people with disabilities like hearing, color blindness, old age and other disadvantaged groups.
• We can screen readers for testing. Some of them are:
  • MAC OS - Voiceover (best with Safari)
  • Windows - JAWS, Narrator, NVDA,
  • LINUX - ORCA
  • Chromevox - Chrome Browser

Q18

✍Make a bouncing ball entirely with help of CSS.

<div class="bouncingball"></div>

.bouncingball {
  width: 140px;
  height: 140px;
  border-radius: 100%;
  background: #CCC;
  animation: bounce 1s;
  transform: translateY(0px);
  animation-iteration-count: infinite;
  position: absolute;
  margin: 50px;
}
@keyframes bounce {
    0% {top: 0;
        -webkit-animation-timing-function: ease-in;
    }
    40% {}
    50% {top: 140px;
        height: 140px;
        -webkit-animation-timing-function: ease-out;
    }
    55% {top: 160px; height: 120px; 
        -webkit-animation-timing-function: ease-in;}
    65% {top: 120px; height: 140px; 
        -webkit-animation-timing-function: ease-out;}
    95% {
        top: 0;        
        -webkit-animation-timing-function: ease-in;
    }
    100% {top: 0;
        -webkit-animation-timing-function: ease-in;
    }
}

Q19

✍In how many ways can CSS be integrated?

You can use the import method or you can put it in as link stylesheet.

<link href="css/bootstrap.min.css" rel="stylesheet">

@import url(“style.css”);

There are 3 methods as to how we can integrate CSS.

1. Inline CSS
2. Within the <head> tag using <style>.
3. Using an external stylesheet (the right way).

Q20

✍What is the difference between visibility: hidden and display: none.

• visibility: hidden hides the content but the space occupied by the content is there.
• display: none removes the space as well.

Q21

✍How to make a triangle in css?

.tri {
    height: 0;
    width: 0;
    border-top: 100px solid green;
    border-bottom: 100px solid transparent;
    border-right: 100px solid transparent;
    border-left: 100px solid transparent;
}

Q22

✍What are data attributes?

• Data Attributes store data in HTML. When you want to call the data, you can use it by CSS (using attr

  <div class="profile" data-name="amrit" data-youtube-name="rat" data-id="1">Profile</div> 
  <style>
  .profile:hover:before { 
    content: attr(data-name); 
    color: red; 
  } 
  </style>
  

Q23

✍What's the difference between "resetting" and "normalizing" CSS? Which would you choose, and why?

• Reset will remove all the default styles applied by the browser to give you a blank canvas.
• Normalize will keep the styles of the default elements consistent across the browsers.

Q24

✍Describe Floats and how they work.

• The float property is used for positioning and layout on web pages. Normally it is used to wrap text around images.
• But you need clear property after using .float.
• If an element is taller than the element containing it, and it is floated, it will overflow outside of its container. So, I use the .clearfix class to remove the float.

Q25

✍Describe z-index and how stacking context is formed.

• The z-index property specifies the stack order of an element. An element with greater stack order is always in front of an element with a lower stack order. z-index: 9999;
• Note: z-index only works on positioned elements (position: absolute, position: relative, or position: fixed).

Q26

✍What are the various clearing techniques and which is appropriate for what context?

• You can use clear: both
• You can use overflow property like overflow: auto;
• .clearfix can also be used

Q27

✍Div property: Difference between div p, div > p, div + p and div ~ p

Q28

✍How font-face is used.

@font-face {
    font-family: myFirstFont;
    src: url(sansation_light.woff);
    Font-weight: bold;
}

You can find the entire file in the below link: github.com/aamrits/interview-questions-prep..