<!-- HTML !-->
<button class="button-42" role="button">Button 42</button>

/* CSS */
.button-42 {
  background-color: initial;
  background-image: linear-gradient(-180deg, #FF7E31, #E62C03);
  border-radius: 6px;
  box-shadow: rgba(0, 0, 0, 0.1) 0 2px 4px;
  color: #FFFFFF;
  cursor: pointer;
  display: inline-block;
  font-family: Inter,-apple-system,system-ui,Roboto,"Helvetica Neue",Arial,sans-serif;
  height: 40px;
  line-height: 40px;
  outline: 0;
  overflow: hidden;
  padding: 0 20px;
  pointer-events: auto;
  position: relative;
  text-align: center;
  touch-action: manipulation;
  user-select: none;
  -webkit-user-select: none;
  vertical-align: top;
  white-space: nowrap;
  width: 100%;
  z-index: 9;
  border: 0;
  transition: box-shadow .2s;
}

.button-42:hover {
  box-shadow: rgba(253, 76, 0, 0.5) 0 3px 8px;
}

<!-- HTML !-->
<button class="button-89" role="button">Button 89</button>

/* CSS */
.button-89 {
  --b: 3px;   /* border thickness */
  --s: .45em; /* size of the corner */
  --color: #373B44;
  
  padding: calc(.5em + var(--s)) calc(.9em + var(--s));
  color: var(--color);
  --_p: var(--s);
  background:
    conic-gradient(from 90deg at var(--b) var(--b),#0000 90deg,var(--color) 0)
    var(--_p) var(--_p)/calc(100% - var(--b) - 2*var(--_p)) calc(100% - var(--b) - 2*var(--_p));
  transition: .3s linear, color 0s, background-color 0s;
  outline: var(--b) solid #0000;
  outline-offset: .6em;
  font-size: 16px;

  border: 0;

  user-select: none;
  -webkit-user-select: none;
  touch-action: manipulation;
}

.button-89:hover,
.button-89:focus-visible{
  --_p: 0px;
  outline-color: var(--color);
  outline-offset: .05em;
}

.button-89:active {
  background: var(--color);
  color: #fff;
}

.button-53 {
  background-color: #3DD1E7;
  border: 0 solid #E5E7EB;
  box-sizing: border-box;
  color: #000000;
  display: flex;
  font-family: ui-sans-serif,system-ui,-apple-system,system-ui,"Segoe UI",Roboto,"Helvetica Neue",Arial,"Noto Sans",sans-serif,"Apple Color Emoji","Segoe UI Emoji","Segoe UI Symbol","Noto Color Emoji";
  font-size: 1rem;
  font-weight: 700;
  justify-content: center;
  line-height: 1.75rem;
  padding: .75rem 1.65rem;
  position: relative;
  text-align: center;
  text-decoration: none #000000 solid;
  text-decoration-thickness: auto;
  width: 100%;
  max-width: 460px;
  position: relative;
  cursor: pointer;
  transform: rotate(-2deg);
  user-select: none;
  -webkit-user-select: none;
  touch-action: manipulation;
}

.button-53:focus {
  outline: 0;
}

.button-53:after {
  content: '';
  position: absolute;
  border: 1px solid #000000;
  bottom: 4px;
  left: 4px;
  width: calc(100% - 1px);
  height: calc(100% - 1px);
}

.button-53:hover:after {
  bottom: 2px;
  left: 2px;
}

@media (min-width: 768px) {
  .button-53 {
    padding: .75rem 3rem;
    font-size: 1.25rem;
  }
}

.glow-on-hover {
    width: 220px;
    height: 50px;
    border: none;
    outline: none;
    color: #fff;
    background: #111;
    cursor: pointer;
    position: relative;
    z-index: 0;
    border-radius: 10px;
}

.glow-on-hover:before {
    content: '';
    background: linear-gradient(45deg, #ff0000, #ff7300, #fffb00, #48ff00, #00ffd5, #002bff, #7a00ff, #ff00c8, #ff0000);
    position: absolute;
    top: -2px;
    left:-2px;
    background-size: 400%;
    z-index: -1;
    filter: blur(5px);
    width: calc(100% + 4px);
    height: calc(100% + 4px);
    animation: glowing 20s linear infinite;
    opacity: 0;
    transition: opacity .3s ease-in-out;
    border-radius: 10px;
}

.glow-on-hover:active {
    color: #000
}

.glow-on-hover:active:after {
    background: transparent;
}

.glow-on-hover:hover:before {
    opacity: 1;
}

.glow-on-hover:after {
    z-index: -1;
    content: '';
    position: absolute;
    width: 100%;
    height: 100%;
    background: #111;
    left: 0;
    top: 0;
    border-radius: 10px;
       color: #fff;

}

@keyframes glowing {
    0% { background-position: 0 0; }
    50% { background-position: 400% 0; }
    100% { background-position: 0 0; }
}