progress {
  -webkit-appearance: none;

  &::-webkit-progress-bar {
    background-color: var(--alt-background-color);
  }

  &::-webkit-progress-value {
    background-color: var(--text-color);
  }
}

progress {
  -webkit-appearance: none;
  height: 10px;
  background-color: var(--alt-background-color);

  &::-webkit-progress-bar {
    background-color: transparent;
  }

  &::-webkit-progress-value {
    background-color: var(--text-color);
  }

  &:indeterminate {
    background-image:
       -webkit-linear-gradient(-45deg, transparent 33%, var(--text-color) 33%,
                               var(--text-color) 66%, transparent 66%);
    background-size: 25px 10px, 100% 100%, 100% 100%;

    -webkit-animation: progress-indeterminate-animation 5s linear infinite;
  }
}

@-webkit-keyframes progress-indeterminate-animation {
   100% { background-position: 100px 0px; }
}

Add styling for indeterminate progress, h/t simurai
Add styling for indeterminate progress, h/t simurai
