@import url(https://fonts.googleapis.com/css?family=Raleway:300);

$anim-duration: 5; // in seconds
$anim-speed: 0.65; // in seconds

:root {
  --btn-border: 1px solid rgba(255, 255, 255, 0.2);
  --btn-bg: transparent; // #333
  --btn-shadow: 1px 1px 25px 10px rgba(255, 255, 255, 0.5);
  --btn-text-color: #f4f4f4;

  --shine-degree: 120deg;
  --shine-color: rgba(255, 255, 255, 0.2);
  --shine-effect: linear-gradient(
    var(--shine-degree),
    transparent,
    var(--shine-color),
    transparent
  );
  --shine-transition: all #{$anim-speed}s ease-in-out;
}

.btn {
  position: relative;
  overflow: hidden; // debug

  // last element should not have margin
  &:not(:last-child) {
    margin-bottom: 3rem;
  }
  font-size: 1.1rem;
  padding: 1rem 3rem;

  border-radius: 4px;
  text-decoration: none;
  border: var(--btn-border);
  color: var(--btn-text-color);
  background: var(--btn-bg);

  &::before {
    content: "";
    position: absolute;
    top: 0;
    width: 100%;
    height: 100%;
    background: var(--shine-effect);
  }
}

.btn-hover {
  &::before {
    left: -100%;
    transition: var(--shine-transition);
  }

  &:hover {
    box-shadow: var(--btn-shadow);

    &::before {
      left: 100%;
    }
  }
}

.btn-anim {
  &::before {
    animation: shine #{$anim-duration}s ease-in-out infinite;
  }
}

@keyframes shine {
  0% {
    left: -100%;
    transition-property: left;
  }
  #{($anim-speed / ($anim-duration + $anim-speed) * 100%)},
  100% {
    left: 100%;
    transition-property: left;
  }
}

.btn-alt {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 250px;
  height: 60px;
  font-size: 1.1rem;

  position: relative;
  overflow: hidden; // debug

  // last element should not have margin
  &:not(:last-child) {
    margin-bottom: 3rem;
  }
  border-radius: 4px;
  text-decoration: none;
  border: var(--btn-border);
  color: var(--btn-text-color);
  background: var(--btn-bg);

  &::before,
  &::after {
    content: "";
    display: block;
    position: absolute;
    height: 100%;
    top: 0;
  }
  &:before {
    background: rgba(255, 255, 255, 0.5);
    width: 60px;
    left: 0;
    filter: blur(30px);
    animation: shine-alt1 #{$anim-duration}s ease-in-out infinite;
  }
  &:after {
    background: rgba(255, 255, 255, 0.2);
    width: 30px;
    left: 30px;
    filter: blur(5px);
    animation: shine-alt2 #{$anim-duration}s ease-in-out infinite;
  }
}

@keyframes shine-alt1 {
  0% {
    opacity: 0.5;
    transform: translateX(-100px) skewX(-15deg);
    transition-property: opacity, transform;
  }
  #{($anim-speed / ($anim-duration + $anim-speed) * 100%)},
  100% {
    opacity: 0.6;
    transform: translateX(300px) skewX(-15deg);
    transition-property: opacity, transform;
  }
}

@keyframes shine-alt2 {
  0% {
    opacity: 0;
    transform: translateX(-100px) skewX(-15deg);
    transition-property: opacity, transform;
  }
  #{($anim-speed / ($anim-duration + $anim-speed) * 100%)},
  100% {
    opacity: 1;
    transform: translateX(300px) skewX(-15deg);
    transition-property: opacity, transform;
  }
}