Non-standard
This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
The ::-ms-expand CSS pseudo-element is a Microsoft extension that represents the button of a <select> menu control that opens or closes the drop-down menu. Typically it is a triangle that points downward.
Only the following CSS properties can be used in a rule with ::-ms-expand in its selector. Other properties are ignored.
background-clipbackground-colorbackground-imagebackground-originbackground-repeatbackground-sizeborder-bottom-colorborder-bottom-left-radiusborder-bottom-right-radiusborder-bottom-styleborder-bottom-widthborder-left-colorborder-left-styleborder-left-widthborder-right-colorborder-right-style border-right-widthborder-top-colorborder-top-left-radiusborder-top-right-radius border-top-styleborder-top-widthbox-shadowbox-sizingcolorcursordisplay (values block, inline-block, none)@font-facefont-sizefont-stylefont-weightheightmargin-bottommargin-leftmargin-rightmargin-top-ms-background-position-x-ms-background-position-y-ms-high-contrast-adjustopacityoutline-coloroutline-styleoutline-widthpadding-bottompadding-leftpadding-rightpadding-toptransformtransform-originvisibilitywidth::-ms-expand
Not part of any specification.
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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/CSS/::-ms-expand