How to fill a rotating background with responsive layout in CSS?

When rotating a element inside a div, or fullscreen, if you know the dimensions you can make it wide or tall enough to hide it by making the inner element bounds. With responsive web design, this seem to be a issue when height/width is too far off each other where the diagonal becomes too long.

Here is a example of an rotating background pattern that works in some aspects, but once it goes too tall or too wide it breaks and green background color bleeds: Codepen

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-css -->

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  width: 100vw;
  height: 100vh;
  overflow: hidden;
  background: green;
}

.pattern {
  width: 200%;
  height: 200%;
  position: fixed;
  top: -50%;
  right: -50%;
  background-image: conic-gradient( white 0deg 45deg, black 45deg 90deg, white 90deg 135deg, black 135deg 180deg, white 180deg 225deg, black 225deg 270deg, white 270deg 315deg, black 315deg 360deg);
  animation: rotate 4s linear infinite;
}

@keyframes rotate {
  0% {
    transform: rotate(0);
  }
  0% {
    transform: rotate(1turn);
  }
}

<!-- language: lang-html -->

<div class="pattern"></div>

<!-- end snippet -->

See this solution, max takes the highest value of 100vh or 100vw, adds it to a variable and adds it to the width and height, I made some other changes to make it work as expected:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-css -->

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
 }
body {
  width: 100vw;
  height: 100vh;
  overflow: hidden;
  background: green;
}
.pattern {
  --size: calc(100vmax * 1.5);
  width: var(--size);
  height: var(--size);
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  background-image: conic-gradient(
    white 0deg 45deg,
    black 45deg 90deg,
    white 90deg 135deg,
    black 135deg 180deg,
    white 180deg 225deg,
    black 225deg 270deg,
    white 270deg 315deg,
    black 315deg 360deg
  );
  animation: rotate 4s linear infinite;
}
@keyframes rotate {
  0% {
    transform: translate(-50%, -50%) rotate(0);
  }
  0% {
    transform: translate(-50%, -50%) rotate(360deg);
  }
}

<!-- language: lang-html -->

<div class="pattern"></div>

<!-- end snippet -->

Your code can be simplified like below. All you need a big negative value with inset

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-css -->

body {
  background: green;
}

.pattern {
  position: fixed;
  inset: -200vmax;
  background: repeating-conic-gradient(white 0 12.5%, black 0 25%);
  animation: rotate 4s linear infinite;
}

@keyframes rotate {
  0% {
    transform: rotate(1turn);
  }
}

<!-- language: lang-html -->

<div class="pattern"></div>

<!-- end snippet -->

This stays responsive under normal conditions - if device isn't narrow and super long. I have added @media for narrower width, otherwise I couldn't get it to work better. I'm curious if there is a better solution to it!

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-css -->

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  width: 100vw;
  height: 100vh;
  overflow: hidden;
  background: green;
  display: flex;
  justify-content: center;
  align-items: center;
}

.pattern {
  width: 200vw;
  min-width: 200vh;
  height: 200vw;
  min-heigth: 200vh;
  position: fixed;
 
  background-image: conic-gradient(
    white 0deg 45deg,
    black 45deg 90deg,
    white 90deg 135deg,
    black 135deg 180deg,
    white 180deg 225deg,
    black 225deg 270deg,
    white 270deg 315deg,
    black 315deg 360deg
  );
  background-size: cover;
  animation: rotate 4s linear infinite;
}

@media screen and (max-width: 640px){
  .pattern {
    width: 400vh;
    min-width: 400vh;
    height: 400vw;
    min-height: 400vw;
  }
}

@keyframes rotate {
  0% {
    transform: rotate(0);
  }
  0% {
    transform: rotate(1turn);
  }
}

<!-- language: lang-html -->

<div class="pattern"></div>

<!-- end snippet -->

Hopefully it helps!