CSS selector based on a condition

Question

I am trying to get a CSS selector to check and apply the CSS based on the condition that if: sectionContent-noToolbar is available, then apply height:2em

Answer 1

No, it isn't.

If they were siblings, then you could use the adjacent sibling combinator:

.sectionContent-noToolbar + .sectionSeperator {
    height: 2em;
}

… but CSS has nothing that lets you modify an element based on its siblings descendants.