html,
body {
    height: 100%;
}

body {
    display: grid;
    place-content: center;
}

.btn {
    background: hsl(var(--hue), 98%, 80%);
    border: none;
    border-radius: 7px;
    cursor: pointer;
    color: black;
    font: 600 1.05rem/1 "Nunito", sans-serif;
    letter-spacing: 0.05em;
    overflow: hidden;
    padding: 1.15em 3.5em;
    min-height: 3.3em;
    position: relative;
    text-transform: lowercase;
}

.btn--yellow {
    --hue: 46;
}

.btn--green {
    --hue: 163;
}

.btn--purple {
    --hue: 244;
}

.btn--red {
    --hue: 0;
}

.btn--blue {
    --hue: 210;
}

.btn:active,
.btn:focus {
    outline: 3px solid hsl(calc(var(--hue) + 90), 98%, 80%);
}

.btn+.btn {
    margin-top: 2.5em;
}

.btn__txt {
    position: relative;
    z-index: 2;
}

.btn__bg {
    background: hsl(var(--hueBg), 98%, 80%);
    border-radius: 50%;
    display: block;
    height: 0;
    left: 50%;
    margin: -50% 0 0 -50%;
    padding-top: 100%;
    position: absolute;
    top: 50%;
    width: 100%;
    transform: scale(0);
    transform-origin: 50% 50%;
    transition: transform 0.2s cubic-bezier(0.5, 1, 0.89, 1);
    z-index: 1;
}

.btn__bg:nth-of-type(1) {
    --hueBg: calc(var(--hue) - 90);
    transition-delay: 0.1875s;
}

.btn__bg:nth-of-type(2) {
    --hueBg: calc(var(--hue) - 180);
    transition-delay: 0.125s;
}

.btn__bg:nth-of-type(3) {
    --hueBg: calc(var(--hue) - 270);
    transition-delay: 0.0625s;
}

.btn__bg:nth-of-type(4) {
    --hueBg: calc(var(--hue) - 360);
    transition-delay: 0s;
}

.btn:hover .btn__bg,
.btn:focus .btn__bg,
.btn:active .btn__bg {
    transform: scale(1.5);
    transition: transform 0.4s cubic-bezier(0.11, 0, 0.5, 0);
}

.btn:hover .btn__bg:nth-of-type(1),
.btn:focus .btn__bg:nth-of-type(1),
.btn:active .btn__bg:nth-of-type(1) {
    transition-delay: 0.125s;
}

.btn:hover .btn__bg:nth-of-type(2),
.btn:focus .btn__bg:nth-of-type(2),
.btn:active .btn__bg:nth-of-type(2) {
    transition-delay: 0.25s;
}

.btn:hover .btn__bg:nth-of-type(3),
.btn:focus .btn__bg:nth-of-type(3),
.btn:active .btn__bg:nth-of-type(3) {
    transition-delay: 0.375s;
}

.btn:hover .btn__bg:nth-of-type(4),
.btn:focus .btn__bg:nth-of-type(4),
.btn:active .btn__bg:nth-of-type(4) {
    transition-delay: 0.5s;
}