The better way to do this is design your classes to target elements and ADD/REMOVE the parent class (v1)
Alternatively, you can use msg props and apply the class per element (harder to maintain) (v2)

Example Flow (use CTRL-I to import)
[{"id":"0dd806ee26fa4c52","type":"ui-template","z":"a95e9b94b8531275","group":"e1c6e6cb771c2108","page":"","ui":"","name":"","order":2,"width":0,"height":0,"head":"","format":"<div style=\"position: relative; width: 190px; height: 40px;\">\n <div class=\"energy-line\" style=\"position: absolute; width: 190px; height: 5px; background-color: #888;\">\n <div :class=\"msg?.payload === true ? 'glow-dot' : ''\" style=\"animation-delay: 0s;\"></div>\n <div :class=\"msg?.payload === true ? 'glow-dot' : ''\" style=\"animation-delay: 0.2s;\"></div>\n <div :class=\"msg?.payload === true ? 'glow-dot' : ''\" style=\"animation-delay: 0.4s;\"></div>\n <div :class=\"msg?.payload === true ? 'glow-dot' : ''\" style=\"animation-delay: 0.6s;\"></div>\n <div :class=\"msg?.payload === true ? 'glow-dot' : ''\" style=\"animation-delay: 0.8s;\"></div>\n <div :class=\"msg?.payload === true ? 'glow-dot' : ''\" style=\"animation-delay: 1s;\"></div>\n <div :class=\"msg?.payload === true ? 'glow-dot' : ''\" style=\"animation-delay: 1.2s;\"></div>\n <div :class=\"msg?.payload === true ? 'glow-dot' : ''\" style=\"animation-delay: 1.4s;\"></div>\n <div :class=\"msg?.payload === true ? 'glow-dot' : ''\" style=\"animation-delay: 1.6s;\"></div>\n <div :class=\"msg?.payload === true ? 'glow-dot' : ''\" style=\"animation-delay: 1.8s;\"></div>\n </div>\n</div>\n","storeOutMessages":true,"passthru":true,"resendOnRefresh":true,"templateScope":"local","className":"","x":2280,"y":1440,"wires":[[]]},{"id":"aba8e40397501c8c","type":"inject","z":"a95e9b94b8531275","name":"","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"true","payloadType":"bool","x":2110,"y":1420,"wires":[["0dd806ee26fa4c52"]]},{"id":"d2f691ed89666e26","type":"inject","z":"a95e9b94b8531275","name":"","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"false","payloadType":"bool","x":2110,"y":1460,"wires":[["0dd806ee26fa4c52"]]},{"id":"65f8825abfc91437","type":"comment","z":"a95e9b94b8531275","name":"V2 - use payload to condition application of styles","info":"","x":2220,"y":1380,"wires":[]},{"id":"fbbb671ac878f4b1","type":"ui-template","z":"a95e9b94b8531275","group":"e1c6e6cb771c2108","page":"","ui":"","name":"","order":1,"width":0,"height":0,"head":"","format":"<div style=\"position: relative; width: 190px; height: 40px;\">\n <div class=\"energy-line\" style=\"position: absolute; width: 190px; height: 5px; background-color: #888;\">\n <div style=\"animation-delay: 0s;\"></div>\n <div style=\"animation-delay: 0.2s;\"></div>\n <div style=\"animation-delay: 0.4s;\"></div>\n <div style=\"animation-delay: 0.6s;\"></div>\n <div style=\"animation-delay: 0.8s;\"></div>\n <div style=\"animation-delay: 1s;\"></div>\n <div style=\"animation-delay: 1.2s;\"></div>\n <div style=\"animation-delay: 1.4s;\"></div>\n <div style=\"animation-delay: 1.6s;\"></div>\n <div style=\"animation-delay: 1.8s;\"></div>\n </div>\n</div>\n","storeOutMessages":true,"passthru":true,"resendOnRefresh":true,"templateScope":"local","className":"","x":2280,"y":1280,"wires":[[]]},{"id":"f5b0d6b0d66d09ae","type":"inject","z":"a95e9b94b8531275","name":"power-on","props":[{"p":"ui_update.class","v":"power-on","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","x":2120,"y":1260,"wires":[["fbbb671ac878f4b1"]]},{"id":"43842466d5f67121","type":"ui-template","z":"a95e9b94b8531275","group":"","page":"","ui":"03482f22997a66ac","name":"Styles","order":0,"width":0,"height":0,"head":"","format":"\n.energy-line {\n position: relative;\n overflow: hidden;\n}\n\n/* target via power-on class and selectors - v1 */\n.power-on .energy-line > div {\n position: absolute;\n top: -3px;\n left: -10px;\n width: 10px;\n height: 10px;\n background-color: rgba(255, 255, 255, 0.5);\n box-shadow: 0 0 5px 3px rgba(0, 148, 206, 0.8);\n border-radius: 50%;\n animation: energy-flow 2s linear infinite;\n display: block;\n}\n\n/* applied manually v2 */\n.glow-dot {\n position: absolute;\n top: -3px;\n left: -10px;\n width: 10px;\n height: 10px;\n background-color: rgba(255, 255, 255, 0.5);\n box-shadow: 0 0 5px 3px rgba(0, 148, 206, 0.8);\n border-radius: 50%;\n animation: energy-flow 2s linear infinite;\n display: block;\n}\n\n@keyframes energy-flow {\n from {\n left: -10px;\n }\n\n to {\n left: 190px;\n }\n}","storeOutMessages":true,"passthru":true,"resendOnRefresh":true,"templateScope":"site:style","className":"","x":2090,"y":1160,"wires":[[]]},{"id":"482d604a41e78e76","type":"comment","z":"a95e9b94b8531275","name":"V1 - add/remove class","info":"","x":2140,"y":1220,"wires":[]},{"id":"56a508ad831ffd27","type":"inject","z":"a95e9b94b8531275","name":"power-off","props":[{"p":"ui_update.class","v":"power-off","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","x":2120,"y":1300,"wires":[["fbbb671ac878f4b1"]]},{"id":"5287694cbe1d19a3","type":"comment","z":"a95e9b94b8531275","name":"Define CSS separatly so it \\n can be used in other templates","info":"","x":2170,"y":1100,"wires":[]},{"id":"e1c6e6cb771c2108","type":"ui-group","name":"test","page":"cf478244c05a3ad7","width":"12","height":1,"order":1,"showTitle":false,"className":"","visible":"true","disabled":"false","groupType":"default"},{"id":"03482f22997a66ac","type":"ui-base","name":"My Dashboard","path":"/dashboard","appIcon":"","includeClientData":true,"acceptsClientConfig":["ui-notification","ui-control"],"showPathInSidebar":false,"headerContent":"page","navigationStyle":"default","titleBarStyle":"default","showReconnectNotification":true,"notificationDisplayTime":1,"showDisconnectNotification":true,"allowInstall":false},{"id":"cf478244c05a3ad7","type":"ui-page","name":"Tasks","ui":"03482f22997a66ac","path":"/pagex","icon":"home","layout":"grid","theme":"6cf98fc8cedde7c6","breakpoints":[{"name":"Default","px":"0","cols":"3"},{"name":"Tablet","px":"576","cols":"6"},{"name":"Desktop","px":"1024","cols":"12"}],"order":1,"className":"","visible":true,"disabled":false},{"id":"6cf98fc8cedde7c6","type":"ui-theme","name":"Green","colors":{"surface":"#ffffff","primary":"#01bb0c","bgPage":"#eeeeee","groupBg":"#ffffff","groupOutline":"#b1dd8c"},"sizes":{"density":"comfortable","pagePadding":"12px","groupGap":"12px","groupBorderRadius":"9px","widgetGap":"18px"}},{"id":"be814b4cb5622085","type":"global-config","env":[],"modules":{"@flowfuse/node-red-dashboard":"1.28.0"}}]