Envelope

<button class="btn-sig-envelope" type="button">
  <span class="btn-sig-envelope__letter" aria-hidden="true"></span>
  <span class="btn-sig-envelope__body">Send it</span>
  <span class="btn-sig-envelope__flap" aria-hidden="true"></span>
</button>

.btn-sig-envelope {
  --btn-bg: #ff8a5c;
  --btn-fg: #26252c;
  --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: 6px;
  --btn-shadow: none;
  --btn-speed: 260ms;
}

.btn-sig-envelope {
  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: 0;
  font-family: var(--btn-font);
  font-size: var(--btn-size);
  font-weight: var(--btn-weight);
  line-height: 1.2;
  color: var(--btn-fg);
  background: transparent;
  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;
  isolation: isolate;
  perspective: 500px;
}

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

.btn-sig-envelope:disabled {
  opacity: 0.5;
  pointer-events: none;
}

.btn-sig-envelope__icon {
  width: 1.15em;
  height: 1.15em;
  flex-shrink: 0;
}

.btn-sig-envelope:hover {
  --rise: -26px;
  --open: 180deg;
  --layer: 0;
}

.btn-sig-envelope__letter {
  position: absolute;
  top: 6px;
  left: 10%;
  right: 10%;
  height: 70%;
  z-index: 1;
  background: repeating-linear-gradient(180deg, transparent 0 6px, #d9d9e3 6px 8px) 8px 8px / calc(100% - 16px) 100% no-repeat, #ffffff;
  border-radius: 3px;
  transform: translateY(var(--rise, 0));
  transition: transform var(--btn-speed) ease;
}

.btn-sig-envelope__body {
  position: relative;
  z-index: 2;
  padding: calc(var(--btn-py) + 18px) calc(var(--btn-px) + 8px) var(--btn-py);
  background: var(--btn-bg);
  border-radius: var(--btn-radius);
}

.btn-sig-envelope__flap {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 28px;
  z-index: var(--layer, 3);
  background: color-mix(in srgb, var(--btn-bg) 82%, #000);
  clip-path: polygon(0 0, 100% 0, 50% 100%);
  transform-origin: 50% 0;
  transform: rotateX(var(--open, 0deg));
  transition: transform var(--btn-speed) ease, z-index 0s calc(var(--btn-speed) / 2);
}

@media (prefers-reduced-motion: reduce) {
  .btn-sig-envelope,
  .btn-sig-envelope__letter,
  .btn-sig-envelope__flap {
    animation: none !important;
    transition: none !important;
  }
}

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

import type React from "react";
import "./sig-envelope.css"; // the CSS tab

export function BtnSigEnvelope({ children = "Send it", ...props }: React.ComponentProps<"button">) {
  return (
    <button className="btn-sig-envelope" type="button" {...props}>
      <span className="btn-sig-envelope__letter" aria-hidden="true" />
      <span className="btn-sig-envelope__body">{children}</span>
      <span className="btn-sig-envelope__flap" aria-hidden="true" />
    </button>
  );
}

<button class="relative inline-flex items-center justify-center gap-[0.5em] [box-sizing:border-box] [padding:0] [font-family:inherit] text-[15px] font-[600] [line-height:1.2] text-[#26252c] [background:transparent] [border:0px_solid_#8b6cff] rounded-[6px] [box-shadow:none] cursor-pointer no-underline whitespace-nowrap [transition:all_260ms_ease] isolate [perspective:500px] focus-visible:[outline:2px_solid_#ff8a5c] focus-visible:[outline-offset:2px] disabled:[opacity:0.5] disabled:[pointer-events:none] hover:[--rise:-26px] hover:[--open:180deg] hover:[--layer:0] motion-reduce:[transition:none!important]" type="button">
  <span class="absolute [top:6px] [left:10%] [right:10%] h-[70%] [z-index:1] [background:repeating-linear-gradient(180deg,_transparent_0_6px,_#d9d9e3_6px_8px)_8px_8px_/_calc(100%_-_16px)_100%_no-repeat,_#ffffff] rounded-[3px] [transform:translateY(var(--rise,_0))] [transition:transform_260ms_ease] motion-reduce:[transition:none!important]" aria-hidden="true"></span>
  <span class="relative [z-index:2] [padding:calc(11px_+_18px)_calc(22px_+_8px)_11px] bg-[#ff8a5c] rounded-[6px]">Send it</span>
  <span class="absolute [top:0] [left:0] [right:0] h-[28px] [z-index:var(--layer,_3)] [background:color-mix(in_srgb,_#ff8a5c_82%,_#000)] [clip-path:polygon(0_0,_100%_0,_50%_100%)] [transform-origin:50%_0] [transform:rotateX(var(--open,_0deg))] [transition:transform_260ms_ease,_z-index_0s_calc(260ms_/_2)] motion-reduce:[transition:none!important]" aria-hidden="true"></span>
</button>