Hello,
I saw the screenshots you attached.
1) Please Edit the categories and remove the images for category heading and then try adding a background color to the shop page by editing it.
Screenshot for Clarification:https://gyazo.com/057cadaeb3bacef84d60def9bda72685
2) Please try adding the following Custom CSS in the Custom CSS for Desktop area under Theme Settings >> Custom CSS.
.searchform.wd-style-with-bg input[type="text"]::placeholder {
color: white;
}
3) Please Go to Woodmart >> Header Builder >> Edit header mobile header in the top right. Edit the row and set the color scheme to light.
Screenshot for Clarification: https://gyazo.com/4a55b02be52f43296e7b2e2817a0d4ae
Regards.
Xtemos Studios