How to divide a webpage into four parts using flexbox?

Question

How to divide a webpage into four equal parts using flex box? Something like this website- www.rileyjshaw.com

The columns should be able to stack upon one another on smaller view ports.

Edit/ Update:

So far I've tried this- Should I change the line height? How can I achieve distinct blocks?

/* Grid */

.column {
  flex-basis: 100%;
  width: 50%;
  height: 50%;
  line-height: 200px;
}

@media screen and (min-width: 800px) {
  .row {
    display: flex;
    flex-direction: row;
    flex-wrap: nowrap;
  }
  .column {
    flex: 1;
  }
  ._25 {
    flex: 2.5;
  }
  ._5 {
    flex: 5;
  }
}


/* Style */

body {
  font-family: 'Lato', sans-serif;
  font-size: 1.3em;
  color: #ccc;
  background: #000;
  /*margin-bottom: 70px;*/
}

.column {
  /* padding: 15px;
  border: 1px solid #666;
  margin: 5px 0;*/
  background: #343436;
}

main {
  max-width: 1200px;
  margin: 0 auto;
}

h1,
h2 {
  text-align: center;
}

<div class="row">
  <div class="column">
    50%
  </div>
  <div class="column">
    50%
  </div>
</div>
<div class="row">
  <div class="column">
    50%
  </div>
  <div class="column">
    50%
  </div>
</div>

Answer 1

You can simplify the code and gain the wanted output. Here I removed the row's and used a container. The main benefit with this structure is that you can alter the order of the column's if you find that necessary.

I also choose to use flex-basis instead of flex-grow to make them stay 50% wide no matter their content size.

On wider screens, using the media query, set the column's 50% wide and the container to display: flex; flex-wrap: wrap;.

On narrower screens, and being block elements, they stack on top of each other by default

html, body {
  height: 100%;
  margin: 0;
}
.container {
  height: 100%;
}
.column {
  height: 25%;
}

@media screen and (min-width: 600px) {
  .container {
    display: flex;
    flex-wrap: wrap;
  }
  .column {
    flex-basis: 50%;
    height: 50%;
  }
}


/* general styles */
body {
  font-family: 'Lato', sans-serif;
  font-size: 1.3em;
  color: #ccc;
  background: #000;
  /*margin-bottom: 70px;*/
}

.column {
  padding: 15px;
  /*border: 1px solid #666;*/
  box-sizing: border-box;
}

.column:nth-child(1) {
  background: #5c9;
}
.column:nth-child(2) {
  background: #fb0;
}
.column:nth-child(3) {
  background: #39f;
}
.column:nth-child(4) {
  background: #f33;
}

main {
  max-width: 1200px;
  margin: 0 auto;
}

h1,
h2 {
  text-align: center;
}

<div class="container">
  <div class="column">
    50%
  </div>
  <div class="column">
    50%
  </div>
  <div class="column">
    50%
  </div>
  <div class="column">
    50%
  </div>
</div>

---

If you still need the original markup structure, here is a sample with that too

html, body {
  height: 100%;
  margin: 0;
}
.row {
  height: 50%;
}
.column {
  height: 50%;
}

@media screen and (min-width: 600px) {
  .row {
    display: flex;
  }
  .column {
    flex-basis: 50%;
    height: 100%;
  }
}


/* general styles */
body {
  font-family: 'Lato', sans-serif;
  font-size: 1.3em;
  color: #ccc;
  background: #000;
  /*margin-bottom: 70px;*/
}

.column {
  padding: 15px;
  /*border: 1px solid #666;*/
  box-sizing: border-box;
}

.row:nth-child(1) .column:nth-child(1) {
  background: #5c9;
}
.row:nth-child(1) .column:nth-child(2) {
  background: #fb0;
}
.row:nth-child(2) .column:nth-child(1) {
  background: #39f;
}
.row:nth-child(2) .column:nth-child(2) {
  background: #f33;
}

main {
  max-width: 1200px;
  margin: 0 auto;
}

h1,
h2 {
  text-align: center;
}

<div class="row">
  <div class="column">
    50%
  </div>
  <div class="column">
    50%
  </div>
</div>
<div class="row">
  <div class="column">
    50%
  </div>
  <div class="column">
    50%
  </div>
</div>

---

Updated based on a comment

Centering the column's content can be done with i.e.:

• Flexbox - https://jsfiddle.net/0ns6ofcp/

  .column {
    height: 25%;  
    display: flex;                         /*  added  */
    justify-content: center;               /*  hor. center  */
    align-items: center;                   /*  ver. center  */
  }
  

• Transform - https://jsfiddle.net/0ns6ofcp/1/

  <div class="column">
    <div>50%</div>
  </div>
  
  .column {
    position: relative;                 /*  added property  */
    height: 25%;  
  }
  .column > div {                       /*  added rule  */
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%,-50%);
  }