Inner 亚 - drawn in a contracted 5-stroke form (standalone has 6; the bottom horizontal merges with the cliff). The traditional 嚴 had two mouths 吅 above a body shape; the simplification compressed those into this 亚 silhouette. Pure graphic remnant, not the standalone meaning.
Outer 厂 - a horizontal stroke turning down sharply, picturing an overhanging cliff. Wraps around the upper-left of the inner 亚 silhouette, framing it under the cliff face. The original 嚴 had this stern-cliff imagery feeding 'strict, stern, severe'. Indexed under Kangxi #1 一 via the top horizontal of 厂.
Filed under radical 一 (yī, #1) by convention. 一 is not a separate component in 严, so no strokes are highlighted.
