Swing

<button class="btn-anim-swing" type="button">
  <span>Get started</span>
</button>

.btn-anim-swing {
  --btn-bg: #7c5cff;
  --btn-fg: #ffffff;
  --btn-font: inherit;
  --btn-size: 15px;
  --btn-weight: 600;
  --btn-px: 22px;
  --btn-py: 11px;
  --btn-w: auto;
  --btn-h: auto;
  --btn-bw: 0px;
  --btn-line: #8b6cff;
  --btn-radius: 10px;
  --btn-shadow: none;
  --btn-speed: 180ms;
}

.btn-anim-swing {
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5em;
  box-sizing: border-box;
  width: var(--btn-w);
  height: var(--btn-h);
  padding: var(--btn-py) var(--btn-px);
  font-family: var(--btn-font);
  font-size: var(--btn-size);
  font-weight: var(--btn-weight);
  line-height: 1.2;
  color: var(--btn-fg);
  background: var(--btn-bg);
  border: var(--btn-bw) solid var(--btn-line);
  border-radius: var(--btn-radius);
  box-shadow: var(--btn-shadow);
  cursor: pointer;
  text-decoration: none;
  white-space: nowrap;
  transition: all var(--btn-speed) ease;
  transform-origin: top center;
  animation: btn-swing 2.6s ease-in-out infinite;
}

.btn-anim-swing:focus-visible {
  outline: 2px solid var(--btn-bg);
  outline-offset: 2px;
}

.btn-anim-swing:disabled {
  opacity: 0.5;
  pointer-events: none;
}

.btn-anim-swing__icon {
  width: 1.15em;
  height: 1.15em;
  flex-shrink: 0;
}

@keyframes btn-swing {
  0%, 50%, 100% { transform: rotate(0); }
  12% { transform: rotate(9deg); }
  24% { transform: rotate(-6deg); }
  36% { transform: rotate(3deg); }
}

@media (prefers-reduced-motion: reduce) {
  .btn-anim-swing {
    animation: none !important;
    transition: none !important;
  }
}

// No JavaScript needed: this one is CSS only.

import type React from "react";
import "./anim-swing.css"; // the CSS tab

export function BtnAnimSwing({ children = "Get started", ...props }: React.ComponentProps<"button">) {
  return (
    <button className="btn-anim-swing" type="button" {...props}>
      <span>{children}</span>
    </button>
  );
}

<button class="relative inline-flex items-center justify-center gap-[0.5em] [box-sizing:border-box] [padding:11px_22px] [font-family:inherit] text-[15px] font-[600] [line-height:1.2] text-[#ffffff] bg-[#7c5cff] [border:0px_solid_#8b6cff] rounded-[10px] [box-shadow:none] cursor-pointer no-underline whitespace-nowrap [transition:all_180ms_ease] [transform-origin:top_center] [animation:btn-swing_2.6s_ease-in-out_infinite] focus-visible:[outline:2px_solid_#7c5cff] focus-visible:[outline-offset:2px] disabled:[opacity:0.5] disabled:[pointer-events:none] motion-reduce:[animation:none!important] motion-reduce:[transition:none!important]" type="button">
  <span>Get started</span>
</button>

<!-- A class cannot hold keyframes: keep this in your CSS. -->
<style>
@keyframes btn-swing {
  0%, 50%, 100% { transform: rotate(0); }
  12% { transform: rotate(9deg); }
  24% { transform: rotate(-6deg); }
  36% { transform: rotate(3deg); }
}
</style>