"Tonight" is about a quiet moment of closeness between two people, and the speaker's decision to let it stay wordless. The poem opens with a shrug, almost a question: some things are better left unsaid, and does it matter anyway? What follows answers that. The speaker describes the warmth of a face against their chest and the gentle pressure of a body nearby, physical details that no sentence could improve on.
The feeling here is peace, but a slightly surprised kind. The speaker calls the contentment "so sweet & foreign," which suggests it isn't something they're used to. That unfamiliarity brings a "tremulous urge" to say something, to name the feeling, and the poem shows them catching themselves and returning to the opening idea. The repeated line works like a reminder to stay put.
The mood is hushed and tender. Words like "blend" and "deliquesce" make the couple seem to melt together, and the ending, "nothing else matters," settles into calm.