How do I create semi-transparent borders in CSS?

How to Establish Semi-Transparent Borders in CSS

In CSS, setting the opacity property affects the transparency of the entire element, including its text. For creating semi-transparent borders, a straightforward approach is not available. However, the rgba color format enables you to achieve this effect.

For instance, the following code sets a 50% opaque red border:

div {
    border: 1px solid rgba(255, 0, 0, .5);
    -webkit-background-clip: padding-box; /* for Safari */
    background-clip: padding-box; /* for IE9+, Firefox 4+, Opera, Chrome */
}

For browsers that don't support rgba (IE8 and earlier), a double border strategy is necessary. The first border is set to a fake opacity, while the second represents the actual desired opacity:

div {
    border: 1px solid rgb(127, 0, 0);
    border: 1px solid rgba(255, 0, 0, .5);
    -webkit-background-clip: padding-box; /* for Safari */
    background-clip: padding-box; /* for IE9+, Firefox 4+, Opera, Chrome */
}

The first border simulates a 50% opaque red border over white, creating the desired effect on most browsers.

To ensure the border remains transparent even with a solid background color, add background-clip: padding-box; as shown in the examples above.

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