close-button.css

/*------close button anim-------*/
/* tabs --- rotate close button */

/* size of button */
:root {
    --tab_close_icons_size: 20px !important;
}
#main-window #navigator-toolbox #TabsToolbar #closetab_fmarin_com-browser-action .toolbarbutton-icon,
#main-window #navigator-toolbox #TabsToolbar #_fe8cab45-aaee-45f8-8765-781e0ebea300_-browser-action .toolbarbutton-icon,
#main-window #navigator-toolbox #TabsToolbar .close-icon>.toolbarbutton-icon,
#main-window #navigator-toolbox #TabsToolbar .tab-content .close-icon {
    min-width: var(--tab_close_icons_size) !important;
    width: var(--tab_close_icons_size) !important;
    min-height: var(--tab_close_icons_size) !important;
    height: var(--tab_close_icons_size) !important;
    margin-right: 2px !important;
}

/* icon & anim */
.tab-close-button {
    list-style-image: url("data:image/svg+xml;base64,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") !important;
    background: none !important;
}

#tabbrowser-tabs .tabbrowser-tab:hover .tab-close-button {
    transform: rotate(2880deg) !important;
    transition: transform ease-in-out 4s !important;
}

/* Show Tab Close buttons only when hovered (slide in using max-width) */
.tabbrowser-tab:not([pinned]) .tab-close-button {
    max-width: 0px !important;
    opacity: 0 !important;
    transition: all 250ms ease-in-out 250ms !important;
    /* no delay on exit*/
}

.tabbrowser-tab:not([pinned]):hover .tab-close-button {
    display: -moz-box !important;
    max-width: 20px !important;
    opacity: 1 !important;
    transition: all 250ms ease-in-out 250ms !important;
    /* quarter second delay on entry*/
}

/*changes color of not selected tabs close button*/
.tab-close-button:not([selected]) {
    filter: invert(50%) !important;
}