CSS - gradient border not working in safari

Question

I am trying to create a custom button with a gradient border. At this point I got the button to work in both Chrome and Firefox.

I have followed an online guide on how to create custom borders with a gradient which are also rounded. The link to the guide can be found here: documentation.

But for some reason the same styling does not work in Safari. I do not know why this is the case.

Here is the CSS code I use in order to create the button. I have also included a snippet with the same style at the bottom. Note that the snippet has a few extra classes and CSS properties just to get it to show properly.

.rainbow-gradient-border {
  position: relative;

  border-radius: 0.25rem;
  box-shadow: 0 2px 10px 0 rgba(142, 57, 255, 0.29);
}
.rainbow-gradient-border::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  border-radius: 0.25rem;
  padding: 0.1rem;
  background: linear-gradient(
    90deg,
    #4d3d8f 0%,
    #df67ed 23%,
    #e24c26 65%,
    #f18823 84%,
    #3aa6c2 100%
  );
  -webkit-mask: linear-gradient(#fff 0 0) content-box, linear-gradient(#fff 0 0);
  -webkit-mask-composite: destination-out;
  mask-composite: exclude;
}

body, .container{
 width: 100%;
 height: 100%;
 background-color: black;
}

.container{
 background-color: black;
}

.rainbow-gradient-border {
  position: relative;
  color: white;
  width: 10rem;
  
  display: flex;
  justify-content: center;
  align-items: center;
  
  border-radius: 0.25rem;
  box-shadow: 0 2px 10px 0 rgba(142, 57, 255, 0.29);
}
.rainbow-gradient-border::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  border-radius: 0.25rem;
  padding: 0.1rem;
  background: linear-gradient(
    90deg,
    #4d3d8f 0%,
    #df67ed 23%,
    #e24c26 65%,
    #f18823 84%,
    #3aa6c2 100%
  );
  -webkit-mask: linear-gradient(#fff 0 0) content-box, linear-gradient(#fff 0 0);
  -webkit-mask-composite: destination-out;
  mask-composite: exclude;
}

<div class="container">
  <div class="rainbow-gradient-border">
    <p>Log In</p>
  </div>
</div>

Answer 1

You can achieve this in a more simple way, without using masks. I used this tool to add the prefixes.

   body, .container{
 width: 100%;
 height: 100%;
 background-color: black;
 color: white;
}

.rainbow-gradient-border {
  position: relative;
}

.outie{
  display: inline-block;
    background: -webkit-gradient(
    linear,
    left top, right top,
    from(#4d3d8f),
    color-stop(23%, #df67ed),
    color-stop(65%, #e24c26),
    color-stop(84%, #f18823),
    to(#3aa6c2)
  );
    background: -o-linear-gradient(
    left,
    #4d3d8f 0%,
    #df67ed 23%,
    #e24c26 65%,
    #f18823 84%,
    #3aa6c2 100%
  );
    background: linear-gradient(
    90deg,
    #4d3d8f 0%,
    #df67ed 23%,
    #e24c26 65%,
    #f18823 84%,
    #3aa6c2 100%
  );
  border-radius: 4px;
  padding: 2px;
  width: 10rem;
  border-radius: 0.25rem;
  -webkit-box-shadow: 0 2px 10px 0 rgba(142, 57, 255, 0.29);
          box-shadow: 0 2px 10px 0 rgba(142, 57, 255, 0.29);
}

.innie{
  display:inline-block;
  width: 100%;
  background: black;
  padding: 15px 0px;
  text-align: center;
}

<div class="container">
  <div class="rainbow-gradient-border">
    <span class="outie">
      <span class="innie">
        Log In
      </span>
    </span>
  </div>
</div>