CSS Calc Viewport Units Workaround?

Question 1

Before I answer this, I'd like to point out that Chrome and IE 10+ actually supports calc with viewport units.

FIDDLE (In IE10+)

Solution (for other browsers): box-sizing

1) Start of by setting your height as 100vh.

2) With box-sizing set to border-box - add a padding-top of 75vw. This means that the padding will be part f the inner height.

3) Just offset the extra padding-top with a negative margin-top

FIDDLE

div
{
    /*height: calc(100vh - 75vw);*/
    height: 100vh;
    margin-top: -75vw;
    padding-top: 75vw;
    -moz-box-sizing: border-box;
    box-sizing: border-box;
    background: pink;
}

Question 2

As a workaround you can use the fact percent vertical padding and margin are computed from the container width. It's quite a ugly solution and I don't know if you'll be able to use it but well, it works: http://jsfiddle.net/bFWT9/

<!DOCTYPE html>
<html>
    <head>
        <title></title>
    </head>
    <body>
        <div>It works!</div>
    </body>
</html>

html, body, div {
    height: 100%;
}
body {
    margin: 0;
}
div {
    box-sizing: border-box;
    margin-top: -75%;
    padding-top: 75%;
    background: #d35400;
    color: #fff;
}

Question 3

<div>It's working fine.....</div>

div
{
     height: calc(100vh - 8vw);
    background: #000;
    overflow:visible;
    color: red;
}

Check here this css code right now support All browser without Opera

just check this

Live

see Live preview by jsfiddle

See Live preview by codepen.io

Question 4

Doing this with a CSS Grid is pretty easy. The trick is to set the grid's height to 100vw, then assign one of the rows to 75vw, and the remaining one (optional) to 1fr. This gives you, from what I assume is what you're after, a ratio-locked resizing container.

Example here: https://codesandbox.io/s/21r4z95p7j

You can even utilize the bottom gutter space if you so choose, simply by adding another "item".

Edit: StackOverflow's built-in code runner has some side effects. Pop over to the codesandbox link and you'll see the ratio in action.

body {
  margin: 0;
  padding: 0;
  background-color: #334;
  color: #eee;
}

.main {
  min-height: 100vh;
  min-width: 100vw;
  display: grid;
  grid-template-columns: 100%;
  grid-template-rows: 75vw 1fr;
}

.item {
  background-color: #558;
  padding: 2px;
  margin: 1px;
}

.item.dead {
  background-color: transparent;
}

<html>
  <head>
    <title>Parcel Sandbox</title>
    <meta charset="UTF-8" />
    <link rel="stylesheet" href="src/index.css" />
  </head>

  <body>
    <div id="app">
      <div class="main">
        <div class="item">Item 1</div>
        <!-- <div class="item dead">Item 2 (dead area)</div> -->
      </div>
    </div>
  </body>
</html>