See for example https://fr.wikipedia.org/wiki/Irrigation?useskin=timeless
There are big space between line 1 Techniques d’irrigation and 1.1 Écoulement de surface and others subsections.

I purpose to remove the margin of ul, the render looks better to me, and solve this problem.

#toc ul, .toc ul {
	margin: 1em 0 0;
	list-style: none;
}

Reported on frwiki: https://fr.wikipedia.org/wiki/Discussion_aide:Apparence_Timeless#Espacement_des_sections_dans_le_sommaire