Nút tải về hiệu ứng đẹp

Bước 1: Chèn mã css vào trước </head>

<style>
:root{--dur:3s;--arrowA:polygon(33% 0%,67% 0%,67% 60%,100% 60%,50% 100%,0% 60%,33% 60%);--arrowB:polygon(0% 37.5%,100% 37.5%,100% 62.5%,100% 62.5%,50% 62.5%,0% 62.5%,0% 62.5%);font-size:calc(20px + (40 - 20)*(100vw - 320px)/(2560 - 320));}
button{background:#255ff4;border-radius:0.2em;color:#fff;cursor:pointer;display:flex;margin:auto;padding:0.5em 1em;position:relative;transition:background 0.15s linear;width:10.5em;-webkit-appearance:none;-moz-appearance:none;appearance:none;-webkit-tap-highlight-color:transparent;}
button:focus{outline:transparent;}
button::-moz-focus-inner{border:0;}
button:not(:disabled):focus,button:not(:disabled):hover{background:#0b46da;}
button:not(:disabled):active{transform:translateY(1px);}
button:disabled{cursor:not-allowed;}
button span,button:before,button:after{display:inline-block;pointer-events:none;}
button:before,button:after{border-radius:0.25em;opacity:0;top:1em;left:1.3em;height:0.5em;transform-origin:0.25em 50%;z-index:2;}
button:before{transform:rotate(-180deg);width:0.8em;}
button:after{width:1.2em;}
button:before,button:after,.dl-icon:before,.dl-icon:after{content:"";display:block;position:absolute;}
button:before,button:after,.dl-icon:before{background:currentColor;}
button span + span{margin:auto;}
.dl-icon{margin-right:0.5em;position:relative;width:1.5em;height:1.5em;}
.dl-icon:before{clip-path:var(--arrowA);-webkit-clip-path:var(--arrowA);top:0;left:calc(50% - 0.55em);transform-origin:50% 100%;width:1.1em;height:1em;z-index:1;}
.dl-icon:after{background-image:linear-gradient(#0b46da,#0b46da);background-position:-1.5em 0;background-size:100% 100%;background-repeat:no-repeat;box-shadow:0.25em 0 0 inset,-0.25em 0 0 inset,0 -0.25em 0 inset;bottom:0;width:100%;height:0.5em;}
.dl-working:before{animation:checkOutA var(--dur) linear forwards;}
.dl-working:after{animation:checkOutB var(--dur) linear forwards;}
.dl-working .dl-icon{animation:impact var(--dur) linear forwards;}
.dl-working .dl-icon:before{animation:arrowToBar var(--dur) linear forwards;}
.dl-working .dl-icon:after{animation:trayToBar var(--dur) linear forwards;}
/* Animation */
@keyframes impact{from,15%{transform:translateY(0);}17.5%{transform:translateY(0.25em);}20%,to{transform:translateY(0);}}
@keyframes arrowToBar{from{clip-path:var(--arrowA);-webkit-clip-path:var(--arrowA);}10%{clip-path:var(--arrowB);-webkit-clip-path:var(--arrowB);transform:translateY(0);}15%{clip-path:var(--arrowB);-webkit-clip-path:var(--arrowB);transform:translateY(0.625em);}30%{clip-path:var(--arrowB);-webkit-clip-path:var(--arrowB);opacity:1;transform:translateY(0.125em);}35%,to{clip-path:var(--arrowB);-webkit-clip-path:var(--arrowB);opacity:0;transform:translateY(0.125em);}}
@keyframes trayToBar{from,15%{background-color:transparent;border-radius:0;box-shadow:0.25em 0 0 inset,-0.25em 0 0 inset,0 -0.25em 0 inset;transform:translateY(0);}15.1%{background-color:currentColor;border-radius:0;box-shadow:0 0 0 inset,0 0 0 inset,0 0 0 0.1em inset;transform:translateY(0);}30%{background-color:currentColor;background-position:-1.5em 0;border-radius:0.25em;box-shadow:0 0 0 inset,0 0 0 inset,0 0 0 0.1em inset;transform:translateY(-0.5em);}90%{background-color:currentColor;background-position:0 0;border-radius:0.25em;box-shadow:0 0 0 inset,0 0 0 inset,0 0 0 0.1em inset;opacity:1;transform:translateY(-0.5em);}90.1%,to{background-color:currentColor;background-position:0 0;border-radius:0.25em;box-shadow:0 0 0 inset,0 0 0 inset,0 0 0 0.1em inset;opacity:0;transform:translateY(-0.5em);}}
@keyframes checkOutA{from,90%{opacity:0;transform:translate(0,0) rotate(-180deg);}90.1%{opacity:1;width:0.8em;transform:translate(0,0) rotate(-180deg);}92.5%{opacity:1;width:1em;transform:translate(0,0.5em) rotate(-120deg);}95%,to{opacity:1;width:1em;transform:translate(0,0.375em) rotate(-135deg);}}
@keyframes checkOutB{from,90%{opacity:0;transform:translate(0,0) rotate(0);}90.1%{opacity:1;width:1.2em;transform:translate(0,0) rotate(0);}92.5%{opacity:1;width:1.6em;transform:translate(0,0.5em) rotate(-60deg);}95%,to{opacity:1;width:1.6em;transform:translate(0,0.375em) rotate(-45deg);}}
/* Dark mode */
@media (prefers-color-scheme:dark){body{background:#2e3138;}}
</style>

Bước 2: chèn script trước thẻ đóng thẻ đóng </body>

<script>
//<![CDATA[
document.addEventListener("DOMContentLoaded",function(){
	this.addEventListener("click",e => {
		let tar = e.target;
		if (tar.hasAttribute("data-dl")) {
			let dlClass = "dl-working";
			if (!tar.classList.contains(dlClass)) {
				let lastSpan = tar.querySelector("span:last-child"),
					lastSpanText = lastSpan.textContent,
					timeout = getMSFromProperty("--dur",":root");

				tar.classList.add(dlClass);
				lastSpan.textContent = "Đang tải về";
				tar.disabled = true;

				setTimeout(() => {
					lastSpan.textContent = "Đã xong!";
				},timeout * 0.9);

				setTimeout(() => {
					tar.classList.remove(dlClass);
					lastSpan.textContent = lastSpanText;
					tar.disabled = false;
				},timeout + 1e3);
			}
		}
	});
});
function getMSFromProperty(property,selector) {
	let cs = window.getComputedStyle(document.querySelector(selector)),
		transDur = cs.getPropertyValue(property),
		msLabelPos = transDur.indexOf("ms"),
		sLabelPos = transDur.indexOf("s");

	if (msLabelPos > -1)
		return transDur.substr(0,msLabelPos);
	else if (sLabelPos > -1)
		return transDur.substr(0,sLabelPos) * 1e3;
}
//]]>
</script>

Bước 3: Chèn đoạn mã dưới đây vào nơi bạn cần hiển thị nút tải về trong theme

<button type="button" data-dl="">
<span class="dl-icon"></span><span>Tải về</span>
</button>
<button type="button" data-dl="">
<span class="dl-icon"></span><span>Tải về</span>
</button>