Open Props UI

Appearance

2024-11-12

The ridiculously confusing task of styling a decent-looking progress bar

You would think it's easy. I mean, it's just one teeny tiny, simple progress element!

How hard could it be?
html
<progress></progress>

Let's try to do something basic ​

Can we change the height, width and accent-color?

css
progress {
  accent-color: tomato;
  height: 2rem;
  width: 100%;
}

It works! I don't like that border-radius though. Let's set it to 0!

css
progress {
  accent-color: tomato;
  border-radius: 0;
  height: 2rem;
  width: 100%;
}

Uh-oh. It just... disappeared? Uhm.. ok let's ignore that then.

It became gray, that's weird. How about doing something about that background color instead then?

css
progress {
  accent-color: tomato;
  background-color: yellow;
  height: 2rem;
  width: 100%;
}

Gray, still?! What did I even do? 😱

Pseudo-element heaven ​

Turns out the <progress> element is the forgotten middle child in the browser interop program. Pseudo-elements and classes you'll need to remember to get going are:

  • progress:indeterminate
  • progress::-webkit-progress-bar
  • progress::-moz-progress-bar
  • progress::-webkit-progress-value

Armed with this knowledge - how do we change the background-color of... whatever any of that is?

css
progress::-webkit-progress-bar {
  background-color: yellow;
}
progress::-webkit-progress-value {
  background-color: yellow;
}
progress::-moz-progress-bar {
  background-color: yellow;
}

Nothing happened? Hmm, no, guess it's not that.

The finished version ​

At this point I'm just like... screw it! I tried! (╯°□°)╯︵ ┻━┻

If it's going to be this hard I'll just bypass all that nonsense and do something that's readable and will work regardless of pseudo nonsense!

I ended up reaching for the trusty :after pseudo-element. In this case it also enables me to do some nice animations, so win-win!

css
@layer components.root {
  :where(progress) {
    --_accent-color: var(--primary);
    --_bg-color: var(--surface-tonal);

    appearance: none;
    background-color: var(--_bg-color);
    border-radius: var(--border-radius, 0.25rem);
    border: 0;
    display: inline-block;
    block-size: var(--size-1);
    overflow: hidden;
    position: relative;
    vertical-align: baseline;
    inline-size: 100%;

    &::-webkit-progress-bar {
      border-radius: var(--border-radius, 0.25rem);
      background: none;
    }

    &[value]::-webkit-progress-value {
      background-color: var(--_accent-color);

      @media (prefers-reduced-motion: no-preference) {
        transition: inline-size 0.2s
          var(--ease-out-4, cubic-bezier(0, 0, 0.1, 1));
      }
    }

    &::-moz-progress-bar {
      background-color: var(--_accent-color);
    }
  }

  @media (prefers-reduced-motion: no-preference) {
    progress:indeterminate {
      background-color: var(--_bg-color);

      &::after {
        animation: indeterminate 2s linear infinite;
        background-color: var(--_accent-color);
        content: "";
        inset: 0 auto 0 0;
        position: absolute;
        will-change: inset-inline-start, inset-inline-end;
      }

      &[value]::-webkit-progress-value {
        background-color: transparent;
      }

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

    [dir="rtl"] {
      :where(progress):indeterminate {
        animation-direction: reverse;

        &::after {
          animation-direction: reverse;
        }
      }
    }
  }

  @keyframes indeterminate {
    0% {
      left: -200%;
      right: 100%;
    }
    60% {
      left: 107%;
      right: -8%;
    }
    100% {
      left: 107%;
      right: -8%;
    }
  }
}
html
<progress></progress>

Read more ​