Same escape-time kernel on the CPU (JavaScript) and the GPU (GLSL fragment shader). Zoom deep enough and watch highp float fall apart.
Click float32 breaks and look at the GPU panel: the fine detail turns into blocky pixel stripes. That is the GPU's highp float running out of mantissa bits (~24 of them, ≈ 7 decimal digits). The CPU panel uses IEEE 754 double and keeps going.