custom.css

#main-container :not(.today-queries) .lazy-visibility .color-level > .flex.flex-col > .initial > div > .blocks-container > .lazy-visibility > div > .ls-block, .cp__right-sidebar .color-level .color-level > .flex.flex-col > .initial > div > .blocks-container > .lazy-visibility > div > .ls-block {
    background-color: hsl(var(--cl-background), 0.35);
    border: 0px solid hsl(var(--cl-background), 0.85);
    padding-top: 10px;
    padding-bottom: 10px;
    margin-bottom: 15px;
    border-radius: 4px;
    padding-right: 5px;
}
.color-level {
  background-color: transparent !important;
}
/* replace the word "seed/question/project" in the lines below with whatever keyword you want to target */
/* You will also need to replace the hex-code for the color to whatever color you want */
:is(#main-container, .cp__right-sidebar .color-level) :not(.today-queries) .lazy-visibility .color-level > .flex.flex-col > .initial > div > .blocks-container > .lazy-visibility > div > .ls-block[data-refs-self*='"seed'] {
  background-color: #2e8b5735;
}
:is(#main-container, .cp__right-sidebar .color-level) :not(.today-queries) .lazy-visibility .color-level > .flex.flex-col > .initial > div > .blocks-container > .lazy-visibility > div > .ls-block[data-refs-self*='"question'] {
  background-color: #d2972a35;
}
:is(#main-container, .cp__right-sidebar .color-level) :not(.today-queries) .lazy-visibility .color-level > .flex.flex-col > .initial > div > .blocks-container > .lazy-visibility > div > .ls-block[data-refs-self*='"project'] {
  background-color: #d22a2a35;
}

Next you will want to modify the color of the block.

background-color: #2e8b5735;

I would recommend only modifying the first 6 characters of the color code, this will ensure the background-color you choose will be applied with a low opacity setting so that it's not too over whelming on your current theme colors. To find a color hex code you can check the following site: https://coolors.co/c3de2b