Highly detailed vintage retro vinyl sticker illustration of a chubby contemplative frog sitting cross-legged on top of a textured mushroom cap, gazing upward with philosophical melancholy in its large round eyes, one webbed hand resting under its chin in classic thinker pose. Intricate skin texture with stippling for warty bumps, fine cross-hatching defining the rounded belly, detailed mushroom gills underneath the cap, small grass tufts at the base. Tiny floating thought bubbles or question marks above. Bold curved arched text "OVERTHINKING" above the frog following a half-circle path and "IS MY CARDIO" curving below in matching half-circle, in bold condensed slab serif font. White background, professional black ink illustration, vintage engraving aesthetic, no border, no frame, isolated illustration centered composition.