I am learning responsive design. have finally achieved the results desired with "flex". In testing the page in Chrome, Firefox, and Opera five img links out of six do not load. In Safari they all load. All resources are in the same file so there should be no problem loading.
It has completely flummoxed me.
The "cover.jpg", but none of the "btn_f.tif" or btn_i.tif" do, just in Safari.
index.html
btn_i.tif
btn_f.tif