Hi,
The landing page sections’ backgrounds are configurable through the theme’s color options.
For the CSS tweaking, try the following CSS (the identifiers are relatively self-explanatory):
[.lp-blocks#] .lp-block .lp-block-icon { }
[.lp-blocks#] .lp-block .lp-block-title { }
[.lp-blocks#] .lp-block .lp-block-text { }
and [.lp-boxes-#] .lp-box .lp-box-inside { }
for the entire box element (image and text) or [.lp-boxes-#] .lp-box .lp-box-content { }
for just the part holding the text.
Include the identifiers encased in square brackets to target individual block or box section (and replace #
with the appropriate number), or remove that part to apply to all similar sections.