Remove outdated vendor prefixes from CSS

[Copilot]

The CSS contained vendor prefixes that are obsolete for modern browsers (IE9+ era).

Changes

• Removed -webkit-box-shadow, -moz-box-shadow prefixes (3 instances)
• Removed -webkit-transition, -moz-transition, -ms-transition, -o-transition prefixes
• Replaced ::-moz-selection with standard ::selection pseudo-element

Before

body > div.container {
    -webkit-box-shadow: 0 0 8px 3px #eee;
    -moz-box-shadow: 0 0 8px 3px #eee;
    box-shadow: 0 0 8px 3px #eee;
}

.btn {
    -webkit-transition: background-color 0.3s;
    -moz-transition: background-color 0.3s;
    -ms-transition: background-color 0.3s;
    -o-transition: background-color 0.3s;
    transition: background-color 0.3s;
}

::-moz-selection {
    background: #b3d4fc;
}

After

body > div.container {
    box-shadow: 0 0 8px 3px #eee;
}

.btn {
    transition: background-color 0.3s;
}

::selection {
    background: #b3d4fc;
}

Net: 10 lines removed, no functional changes. All properties supported unprefixed since IE9/IE10 (2011-2012) and Firefox 62+ (2018).

Original prompt

There are some outdated vendor prefixes currently residing in the CSS code. Please fix this issue

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