Flex/Grid, Vanilla JS, Mobile first

Hey, great work on this one. Layout both desktop and mobile is really good. Also, awesome that mobile first worked for you nicely!!

Some suggestions would be:

• Wrapping the whole content in a main tag so that it will have a landmark. Also it would be great if you add a h1 but it will be only for screen reader, so it would have a sr-only class. It could be like <h1>Tip Calculator</h1>. For screen reader
• The alt of the img could be the text inside that image. "splittle" since it's name is already defined in the logo.
• Wrapping the all the radio buttons inside of a fieldset element along with its legend will be really great and make it more accessible for assistive tech. With using this, when a screen reader navigates to the radio buttons, it will announce the legend's text, thus creating a guide for screen reader users. Example would be like:

  <fieldset>
    <legend class="sr-only">Select percentage for tippings</legend>
    {all the radio buttons with their labels}
 </fieldset>

Remember to add a screen reader class to the legend.

• For the "Tip amount" and "Total amount" text, instead of using label on it, use a div or p. label are for input elements.
• Also an addition, this will be really great if you want to support accessibility more. Adding a aria-live on a element so that when a user finalizes their tippings, a screen reader would read out the result of their interaction.

Other than those, well done. Choosing radio buttons on those is really great.