How to fix vh(viewport unit) css in mobile Safari?

There’s a pretty good answer to this across at CSS Tricks – https://css-tricks.com/the-trick-to-viewport-units-on-mobile/

.my-element {
  height: 100vh; /* Fallback for browsers that do not support Custom Properties */
  height: calc(var(--vh, 1vh) * 100);
}

// First we get the viewport height and we multiple it by 1% to get a value for a vh unit
let vh = window.innerHeight * 0.01;
// Then we set the value in the --vh custom property to the root of the document
document.documentElement.style.setProperty('--vh', `${vh}px`);