se/SE/se-lib/UI/SidePanelButton.php.style-anim-close-btn.css

/* Animated close btn: p5-side_panel__close */

.p5-side_panel__close:hover::before, .p5-side_panel__close:hover::after {
	-webkit-transition: -webkit-transform 0.3s;
	transition: -webkit-transform 0.3s;
	transition: transform 0.3s;
	transition: transform 0.3s, -webkit-transform 0.3s;
}
.p5-side_panel__close:hover::before {
	-webkit-transform: rotate(220deg);
		-ms-transform: rotate(220deg);
			transform: rotate(220deg);
}
.p5-side_panel__close:hover::after {
	-webkit-transform: rotate(135deg);
		-ms-transform: rotate(135deg);
			transform: rotate(135deg);
}
.p5-side_panel--is-visible .p5-side_panel__close::before {
	-webkit-animation: cd-close-1 0.6s 0.3s;
			animation: cd-close-1 0.6s 0.3s;
}
.p5-side_panel--is-visible .p5-side_panel__close::after {
	-webkit-animation: cd-close-2 0.6s 0.3s;
			animation: cd-close-2 0.6s 0.3s;
}
@-webkit-keyframes cd-close-1 {
	0%, 50% {
		-webkit-transform: rotate(0deg);
				transform: rotate(0deg);
	}
	100% {
		-webkit-transform: rotate(45deg);
				transform: rotate(45deg);
	}
}

@keyframes cd-close-1 {
	0%, 50% {
		-webkit-transform: rotate(0deg);
				transform: rotate(0deg);
	}
	100% {
		-webkit-transform: rotate(45deg);
				transform: rotate(45deg);
	}
}

@-webkit-keyframes cd-close-2 {
	0%, 50% {
		-webkit-transform: rotate(0deg);
				transform: rotate(0deg);
	}
	100% {
		-webkit-transform: rotate(-45deg);
				transform: rotate(-45deg);
	}
}

@keyframes cd-close-2 {
	0%, 50% {
		-webkit-transform: rotate(0deg);
				transform: rotate(0deg);
	}
	100% {
		-webkit-transform: rotate(-45deg);
				transform: rotate(-45deg);
	}
}