Source/WebCore/Modules/modern-media-controls/controls/button.css

/*
 * Copyright (C) 2016-2017 Apple Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

button {
    position: absolute;
    left: 0;
    border: 0;
    padding: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: transparent !important;
    -webkit-appearance: none;
    -webkit-user-select: none;
    -webkit-tap-highlight-color: transparent;
}

/* Icon */

button > picture {
    background-color: var(--secondary-glyph-color);
    mix-blend-mode: plus-lighter;
    -webkit-mask-size: 100% 100%;
    -webkit-mask-repeat: no-repeat;
    transition: transform 150ms;
    will-change: transform;
    /* Work around webkit.org/b/174565 by making the shrinking button's icon non-interactive */
    pointer-events: none;
}

button:focus {
    outline: none;
}

button:focus > picture {
    background-color: -webkit-focus-ring-color !important;
    mix-blend-mode: normal !important;
}

button.skip-back > picture,
button.play-pause > picture,
button.skip-forward > picture {
    background-color: var(--primary-glyph-color);
}

button.on > picture {
    background-color: white !important;
}

button:active > picture {
    transform: scale(0.89);
}

/* Corner style */

button.corner {
    width: 44px !important;
    height: var(--inline-controls-bar-height) !important;
}

/* Center style */

button.center,
button.small-center {
    left: 50% !important;
    top: 50% !important;
    transform: translate(-50%, -50%);
}

button.center {
    width: 60px !important;
    height: 60px !important;
}

button.small-center {
    width: 31px !important;
    height: 31px !important;
}

button.center > .background-tint,
button.small-center > .background-tint,
button.center > .background-tint > div,
button.small-center > .background-tint > div {
    border-radius: 50%;
}

button.center > picture,
button.small-center > picture {
    position: absolute;
    left: 0;
    top: 0;
    width: 100% !important;
    height: 100% !important;
    transform: scale(0.4);
}

button.center:active > picture,
button.small-center:active > picture {
    transform: scale(0.4) scale(calc(8/9));
}