-webkit-mask-position-y - CSS: Cascading Style Sheets
the -webkit-mask-position-y css property sets the initial vertical position of a mask image.
... /* keyword values */ -webkit-mask-position-y: top; -webkit-mask-position-y: center; -webkit-mask-position-y: bottom; /* <percentage> values */ -webkit-mask-position-y: 100%; -webkit-mask-position-y: -50%; /* <length> values */ -webkit-mask-position-y: 50px; -webkit-mask-position-y: -1cm; /* multiple values values */ -webkit-mask-position-y: 50px, 25%, -3em; /* global values */ -webkit-mask-position-y: inherit; -webkit-mask-position-y: initial; -webkit-mask-position-y: unset; initial value0%applies toall elementsinheritednopercentagesrefer to the size of the box itselfcomputed valuefor <length> the absolute value, otherwise a percentageanimation typediscrete syntax values <length-percentage> a length indicating the position of the top side of the image relative to the box's top padding edge.
...ue0%applies toall elementsinheritednopercentagesrefer to the size of the box itselfcomputed valuefor <length> the absolute value, otherwise a percentageanimation typediscrete formal syntax [ <length-percentage> | top | center | bottom ]#where <length-percentage> = <length> | <percentage> examples vertically positioning a mask image .exampleone { -webkit-mask-image: url(mask.png); -webkit-mask-position-y: bottom; } .exampletwo { -webkit-mask-image: url(mask.png); -webkit-mask-position-y: 25%; } specifications not part of any standard.

WebKit CSS extensions - CSS: Cascading Style Sheets
webkit-prefixed properties on the standards track -webkit-appearance -webkit-font-size-delta -webkit-mask-composite -webkit-mask-position-x -webkit-mask-position-y -webkit-mask-repeat-x -webkit-mask-repeat-y formerly proprietary properties that are now standard note: to maximize the compatibility of your css, you should use the unprefixed standard properties instead of the prefixed ones listed below.
... -webkit-mask-position-x* -webkit-mask-position-y* * supported unprefixed in firefox, with prefix in safari.
...p-left-radius -webkit-border-top-right-radius f -webkit-filter -webkit-flex -webkit-flex-basis -webkit-flex-direction -webkit-flex-flow -webkit-flex-grow -webkit-flex-shrink -webkit-flex-wrap j -webkit-justify-content m -webkit-mask -webkit-mask-clip -webkit-mask-composite* -webkit-mask-image -webkit-mask-origin -webkit-mask-position -webkit-mask-position-x** -webkit-mask-position-y** -webkit-mask-repeat -webkit-mask-size o-p -webkit-order -webkit-perspective -webkit-perspective-origin t -webkit-text-fill-color** -webkit-text-size-adjust -webkit-text-stroke** -webkit-text-stroke-color** -webkit-text-stroke-width** -webkit-transform -webkit-transform-origin -webkit-transition -webkit-transition-delay -webkit-transition-duration -webkit-transition-prope...