Height: 100% or Min-Height: 100% For HTML and Body Elements

height: 100% or min-height: 100% for html and body elements?

If you're trying to apply background images to html and body that fill up the entire browser window, neither. Use this instead:

html {
   height: 100%;
}

body {
   min-height: 100%;
}

My reasoning is given here (where I explain holistically how to apply backgrounds in this manner):

Incidentally, the reason why you have to specify height and min-height to html and body respectively is because neither element has any intrinsic height. Both are height: auto by default. It is the viewport that has 100% height, so height: 100% is taken from the viewport, then applied to body as a minimum to allow for scrolling of content.

The first way, using height: 100% on both, prevents body from expanding with its contents once they start to grow beyond the viewport height. Technically this doesn't prevent the content from scrolling, but it does cause body to leave a gap beneath the fold, which is usually undesirable.

The second way, using min-height: 100% on both, doesn't cause body to expand to the full height of html because min-height with a percentage doesn't work on body unless html has an explicit height.

For the sake of completeness, section 10 of CSS2.1 contains all the details, but it's an extremely convoluted read so you can skip it if you're not interested in anything beyond what I've explained here.

Make body have 100% of the browser height

Try setting the height of the html element to 100% as well.

html, 
body {
    height: 100%;
}

Body looks to its parent (HTML) for how to scale the dynamic property, so the HTML element needs to have its height set as well.

However the content of body will probably need to change dynamically.
Setting min-height to 100% will accomplish this goal.

html {
  height: 100%;
}
body {
  min-height: 100%;
}

Setting html, body with min-height: 100% but also allow it to expand

Just use min-height instead of height on your wrapper:

html,body {  height: 100%;  padding:0;   margin:0;}
.wrapper {  display: flex;  flex-direction: column;  border: 1px solid black;  min-height: 100%;  box-sizing: border-box;}
.body {  flex: 1;  min-height: 300px;}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script><div class="wrapper">  <header style="background-color: lightblue">    header  </header>  <div class="body" style="background-color: orange; opacity: 0.3">    body  </div>  <footer style="background-color: yellow">    footer  </footer></div>

html, body {
  min-height: 100%;
}

html {  height: 100%;}
body {  padding: 1.25em;  background-color: #292c37;  border: 1px solid red;  height: 100%;}
.main-app {  min-height: 100%;  display: grid;  grid-template-rows: auto 1fr auto;  border: 1px solid green;}
header {  background-color: wheat;}
main {  background-color: firebrick;}
footer {  background-color: skyblue;}
header,main,footer {  padding: 1.25em;}

<div class="main-app">  <header>Header</header>  <main>Main</main>  <footer>Footer</footer></div>

html, body {
    height: 100%;
}

body {
    min-height: 100vh;
}