Write maintainable CSS with variables, nesting, mixins, modules, maps, and compiled output.
Lessons
Define reusable %patterns that emit no CSS alone.
Placeholder Selectors is easiest to learn by reading the example, changing it, and observing the result.
// Placeholder emits no CSS until it is extended
%card-base {
border-radius: 8px;
padding: 1rem;
box-shadow: 0 1px 3px #0002;
}
.lesson-card { @extend %card-base; border-top: 3px solid #4f46e5; }
.user-card { @extend %card-base; border-top: 3px solid #10b981; }Practice the Placeholder Selectors example in a small scratch file, then explain what changed and why.