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HTML 

              
                <!-- a string of lights, but they’re wired in parallel instead of serial.

M. Kupietz, https://michaelkupietz.com

Modified from tobyj's original demo at https://codepen.io/tobyj/pen/QjvEex -->

<ul id="lightrope">
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li class="broken"></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
</ul>
<p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p>
There is now an enhanced interactive version of this at <a href="https://codepen.io/kupietz/pen/dPbNywN">https://codepen.io/kupietz/pen/dPbNywN</a> where you can knock the bulbs around with your mouse. Still CSS-only.
!

CSS 

              
                body {background:#fff;}
#lightrope {
  text-align: center;
  white-space: nowrap;
  overflow: hidden;
  position: fixed;
  z-index: 1000;
  margin: -15px 0 0 0;
  padding: 0;
  pointer-events: none;
  width: 100%;
}
#lightrope li {
	transform-origin: top-center;
	border-left:2px solid rgba(0,0,0,.05);
	border-right:2px solid rgba(255,255,255,.5);
  position: relative;
  -webkit-animation-fill-mode: both;
          animation-fill-mode: both;
  -webkit-animation-iteration-count: infinite;
          animation-iteration-count: infinite;
  list-style: none;
  margin: 0;
  padding: 0;
  display: block;
  width: 8px; /* orig 12px */
  height: 18px; /* orig 28px */
  border-radius: 50%;
  margin: 20px 20px 20px 22px;
  display: inline-block;

          animation-duration: 2s;
}
#lightrope li:nth-child(5n+0) { 
  background: aqua;
  box-shadow: 0px 4.6666666667px 24px 3px rgba(0, 255, 255, 0.5);
  -webkit-animation-duration: 0.8s; 
          animation-duration: 0.8s;
}
#lightrope li:nth-child(5n+1) {
  background: #f70094;
  box-shadow: 0px 4.6666666667px 24px 3px #f70094;
  -webkit-animation-duration: .9s; 
          animation-duration: .9s;
}
#lightrope li:nth-child(5n+2) { 
	 background: yellow;
  box-shadow: 0px 4.6666666667px 24px 3px yellow;
  -webkit-animation-duration: 1s;
          animation-duration: 1s;
}
#lightrope li:nth-child(5n+3) { 
	 background: pink;
  box-shadow: 0px 4.6666666667px 24px 3px pink ;
  -webkit-animation-duration: 1.1s;
          animation-duration: 1.1s;
}
#lightrope li:nth-child(5n+4) { 
		 background: orange;
  box-shadow: 0px 4.6666666667px 24px 3px orange ;
  -webkit-animation-duration: 1.2s; 
          animation-duration: 1.2s;
}

#lightrope li:nth-child(4n+0) {
    -webkit-animation-name: flash-1, sway;
    animation-name: flash-1, sway;
    -webkit-animation-duration: inherit, 4.9s;
    animation-duration: inherit, 4.9s;
    -webkit-animation-timing-function: inherit, ease-in-out;
    animation-timing-function: inherit, ease-in-out;
}

#lightrope li:nth-child(4n+1) {
    -webkit-animation-name: flash-2, sway;
    animation-name: flash-2, sway;
    -webkit-animation-duration: inherit, 4.1s;
    animation-duration: inherit, 4.1s;
    -webkit-animation-timing-function: inherit, ease-in-out;
    animation-timing-function: inherit, ease-in-out;
}

#lightrope li:nth-child(4n+2) {
    -webkit-animation-name: flash-3, sway;
    animation-name: flash-3, sway;
    -webkit-animation-duration: inherit, 4.3s;
    animation-duration: inherit, 4.3s;
    -webkit-animation-timing-function: inherit, ease-in-out;
    animation-timing-function: inherit, ease-in-out;
}

#lightrope li:nth-child(4n+3) {
    -webkit-animation-name: flash-4, sway;
    animation-name: flash-4, sway;
    -webkit-animation-duration: inherit, 4.5s;
    animation-duration: inherit, 4.5s;
    -webkit-animation-timing-function: inherit, ease-in-out;
    animation-timing-function: inherit, ease-in-out;
}


#lightrope > li.broken { 
  left: -2px;
		 background: #CCC; 
	border-left:2px solid #BDE;
	border-right:2px solid #DEF;
  box-shadow: none !important ;
	-webkit-animation-name:  none !important ;
          animation-name:  none !important ;
  -webkit-animation-duration: 0 !important; 
          animation-duration: 0 !Important;
	
	transform: rotatez(15deg);
}
#lightrope > li.broken::after {
	transform: rotatez(-15deg) translatey(-7px) !important;
}

#lightrope > li:before {
  content: "";
  position: absolute;
  background: #262;
  width: 5px;
  height: 8px;
  border-radius: 3px;
  top: -4.6666666667px;
  left: -1px;
		border-left:2px solid rgba(0,0,0,.05);
	border-right:2px solid rgba(255,255,255,.5);

}
#lightrope > li::after {
  content: "";
  top: -12px; /*14px for non-wavy original */
  left: -1px;
  position: absolute;
  width: 58px;
  height: 18.6666666667px;
  border-bottom: solid #262 2px;
  border-radius: 50%;

  
	

background:#060;
	/* wavy cord: courtesy https://css-generators.com/wavy-shapes/ */
  --mask:
    radial-gradient(5.66px at 50% calc(100% + 4.2px),#0000 calc(99% - 1px),#000 calc(101% - 1px) 99%,#0000 101%) calc(50% - 6px) calc(50% - 2px + .5px)/12px 4px repeat-x, radial-gradient(5.66px at 50% -4.2px,#0000 calc(99% - 1px),#000 calc(101% - 1px) 99%,#0000 101%) 50% calc(50% + 2px)/12px 4px repeat-x, radial-gradient(7.38px at 50% calc(100% + 5.6px),#0000 calc(99% - 1px),#000 calc(101% - 1px) 99%,#0000 101%) calc(50% - 8px) calc(50% - 2.5px + .5px)/16px 5px repeat-x, radial-gradient(7.38px at 50% -5.6px,#0000 calc(99% - 1px),#000 calc(101% - 1px) 99%,#0000 101%) 50% calc(50% + 2.5px)/16px 5px repeat-x;
  -webkit-mask: var(--mask);
          mask: var(--mask);


}
#lightrope li:last-child:after {
  content: none;
}
#lightrope li:first-child {
  margin-left: -40px;
}

@-webkit-keyframes flash-1 {
  0%, 100% {
    background: #00f7a5;
    box-shadow: 0px 4.6666666667px 24px 3px #00f7a5;
  }
  50% {
    background: rgba(0, 247, 165, 0.4);
    box-shadow: 0px 4.6666666667px 24px 3px rgba(0, 247, 165, 0.2);
  }
}

@keyframes flash-1 {
  0%, 100% {
    background: #00f7a5;
    box-shadow: 0px 4.6666666667px 24px 3px #00f7a5;
  }
  50% {
    background: rgba(0, 247, 165, 0.4);
    box-shadow: 0px 4.6666666667px 24px 3px rgba(0, 247, 165, 0.2);
  }
}
@-webkit-keyframes flash-2 {
  0%, 100% {
    background: #0CF;
    box-shadow: 0px 4.6666666667px 24px 3px #0CF;
  }
  50% {
    background: rgba(0, 255, 255, 0.4);
    box-shadow: 0px 4.6666666667px 24px 3px rgba(0, 255, 255, 0.2);
  }
}
@keyframes flash-2 {
  0%, 100% {
    background: #0CF;
    box-shadow: 0px 4.6666666667px 24px 3px #0CF;
  }
  50% {
    background: rgba(0, 255, 255, 0.4);
    box-shadow: 0px 4.6666666667px 24px 3px rgba(0, 255, 255, 0.2);
  }
}
@-webkit-keyframes flash-3 {
  0%, 100% {
    background: #f76666; 
    box-shadow: 0px 4.6666666667px 24px 3px #f76666;
  }
  50% {
    background: rgba(247, 0, 148, 0.4);
    box-shadow: 0px 4.6666666667px 24px 3px rgba(247, 0, 148, 0.2);
  }
}
@keyframes flash-3 {
  0%, 100% {
    background: #f76666;
    box-shadow: 0px 4.6666666667px 24px 3px #f76666;
  }
  50% {
    background: rgba(247, 0, 148, 0.4);
    box-shadow: 0px 4.6666666667px 24px 3px rgba(247, 0, 148, 0.2);
  }
}
@-webkit-keyframes flash-4 {
  0%, 100% {
    background: #FFEE33;
    box-shadow: 0px 4.6666666667px 24px 3px #FFEE33;
  }
  50% {
    background: rgba(247,247,0, 0.4);
    box-shadow: 0px 4.6666666667px 24px 3px rgba(247,247,0,0.2);
  }
}
@keyframes flash-4 {
  0%, 100% {
    background: #FFEE33;
    box-shadow: 0px 4.6666666667px 24px 3px #FFEE33;
  }
  50% {
    background: rgba(247,247,0, 0.4);
    box-shadow: 0px 4.6666666667px 24px 3px rgba(247,247,0, 0.2);
  }
}



@-webkit-keyframes sway {
    0%, 100% {
        transform: rotate(.5deg);
    }
    50% {
        transform: rotate(-.5deg);
    }
}

@keyframes sway {
    0%, 100% {
        transform: rotate(.5deg);
    }
    50% {
        transform: rotate(-.5deg);
    }
}
!

JS 

              
                // original demo:
// https://codepen.io/tobyj/pen/QjvEex
!
999px

Console