Social Media Dashboard with Theme Switcher

Hi Graham, good job but this needs a bit of work on responsiveness for tablet sized viewport. A few suggestions,

• section element needs a heading.
• The cards inside section imo should be article for better semantics. articles are used for self-contained information and it is appropriate to use them in this case.
• input needs label for accessibility purpose as your report says.

For your question, I prefer using dataset attributes on a container (eg. body). Inside the javascript code, I change this dataset's value based on user's preference and inside the CSS I do something like

:root {
    <your css color variables for light mode>
}
[data-theme="dark"] {
    <your css color variables for dark mode>
}

This is assuming a container such as body has a data-theme attribute. It's only my preference since it needs less js code :)