Google material design elevation system shadows as css. Based on https://material.io/design/environment/elevation.html#default-elevations Exported with Sketchapp from the Google material design theme editor plugin "Baseline" theme.

material-design-shadows.css

/* Shadow 0dp */
box-shadow: none;

/* Shadow 1dp */
box-shadow: 0 1px 1px 0 rgba(0,0,0,0.14), 0 2px 1px -1px rgba(0,0,0,0.12), 0 1px 3px 0 rgba(0,0,0,0.20);

/* Shadow 2dp */
box-shadow: 0 2px 2px 0 rgba(0,0,0,0.14), 0 3px 1px -2px rgba(0,0,0,0.12), 0 1px 5px 0 rgba(0,0,0,0.20);

/* Shadow 3dp */
box-shadow: 0 3px 4px 0 rgba(0,0,0,0.14), 0 3px 3px -2px rgba(0,0,0,0.12), 0 1px 8px 0 rgba(0,0,0,0.20);

/* Shadow 4dp */
box-shadow: 0 4px 5px 0 rgba(0,0,0,0.14), 0 1px 10px 0 rgba(0,0,0,0.12), 0 2px 4px -1px rgba(0,0,0,0.20);

/* Shadow 6dp */
box-shadow: 0 6px 10px 0 rgba(0,0,0,0.14), 0 1px 18px 0 rgba(0,0,0,0.12), 0 3px 5px -1px rgba(0,0,0,0.20);

/* Shadow 8dp */
box-shadow: 0 8px 10px 1px rgba(0,0,0,0.14), 0 3px 14px 2px rgba(0,0,0,0.12), 0 5px 5px -3px rgba(0,0,0,0.20);

/* Shadow 9dp */
box-shadow: 0 9px 12px 1px rgba(0,0,0,0.14), 0 3px 16px 2px rgba(0,0,0,0.12), 0 5px 6px -3px rgba(0,0,0,0.20);

/* Shadow 12dp */
box-shadow: 0 12px 17px 2px rgba(0,0,0,0.14), 0 5px 22px 4px rgba(0,0,0,0.12), 0 7px 8px -4px rgba(0,0,0,0.20);

/* Shadow 16dp */
box-shadow: 0 16px 24px 2px rgba(0,0,0,0.14), 0 6px 30px 5px rgba(0,0,0,0.12), 0 8px 10px -5px rgba(0,0,0,0.20);

/* Shadow 24dp */
box-shadow: 0 24px 38px 3px rgba(0,0,0,0.14), 0 9px 46px 8px rgba(0,0,0,0.12), 0 11px 15px -7px rgba(0,0,0,0.20);

Sass Mixin:

@mixin BoxShadow ($dp) {
    @if $dp==0 {
        box-shadow: none
    }
    @else if $dp==1 {
        box-shadow: 0 1px 1px 0 rgba(0, 0, 0, .14), 0 2px 1px -1px rgba(0, 0, 0, .12), 0 1px 3px 0 rgba(0, 0, 0, .20)
    }
    @else if $dp==2 {
        box-shadow: 0 2px 2px 0 rgba(0, 0, 0, .14), 0 3px 1px -2px rgba(0, 0, 0, .12), 0 1px 5px 0 rgba(0, 0, 0, .20)
    }
    @else if $dp==3 {
        box-shadow: 0 3px 4px 0 rgba(0, 0, 0, .14), 0 3px 3px -2px rgba(0, 0, 0, .12), 0 1px 8px 0 rgba(0, 0, 0, .20)
    }
    @else if $dp==4 {
        box-shadow: 0 4px 5px 0 rgba(0, 0, 0, .14), 0 1px 10px 0 rgba(0, 0, 0, .12), 0 2px 4px -1px rgba(0, 0, 0, .20)
    }
    @else if $dp==6 {
        box-shadow: 0 6px 10px 0 rgba(0, 0, 0, .14), 0 1px 18px 0 rgba(0, 0, 0, .12), 0 3px 5px -1px rgba(0, 0, 0, .20)
    }
    @else if $dp==8 {
        box-shadow: 0 8px 10px 1px rgba(0, 0, 0, .14), 0 3px 14px 2px rgba(0, 0, 0, .12), 0 5px 5px -3px rgba(0, 0, 0, .20)
    }
    @else if $dp==9 {
        box-shadow: 0 9px 12px 1px rgba(0, 0, 0, .14), 0 3px 16px 2px rgba(0, 0, 0, .12), 0 5px 6px -3px rgba(0, 0, 0, .20)
    }
    @else if $dp==12 {
        box-shadow: 0 12px 17px 2px rgba(0, 0, 0, .14), 0 5px 22px 4px rgba(0, 0, 0, .12), 0 7px 8px -4px rgba(0, 0, 0, .20)
    }
    @else if $dp==16 {
        box-shadow: 0 16px 24px 2px rgba(0, 0, 0, .14), 0 6px 30px 5px rgba(0, 0, 0, .12), 0 8px 10px -5px rgba(0, 0, 0, .20)
    }
    @else if $dp==24 {
        box-shadow: 0 24px 38px 3px rgba(0, 0, 0, .14), 0 9px 46px 8px rgba(0, 0, 0, .12), 0 11px 15px -7px rgba(0, 0, 0, .20)
    }
}

Example usage:

.card {
    @include BoxShadow(1);
    background: #fff;
    border-radius: 2px;
    &:hover {
        @include BoxShadow(12)
    }
}

I'd just add this to prevent silent errors:

@mixin BoxShadow ($dp) {
    @if $dp==0 {
   // [...]
   @else {
        @error "Invalid argument for $dp: {" + $dp + "}, look at the method definition for possible values";
    }
}

Where is the /* Shadow 9dp */ elevation use case within material design? I don't see anywhere where it utilizes 9dp based elevation in documentation?

Note that these shadows are out of date. Here are the current ones https://github.com/material-components/material-components-web/blob/master/packages/mdc-elevation/_elevation-theme.scss

I also haven't seen 9dp used anywhere and they defined 24 variants but I think they wanted to have the ability to use levels between if necessary.

Here's the plain CSS I could find after reading @MarkusRodler's comment.

Pulled it from the css file on the example docs: https://material-components.github.io/material-components-web-catalog/#/component/elevation

.mdc-elevation--z0 {
    box-shadow: 0px 0px 0px 0px rgba(0, 0, 0, 0.2), 0px 0px 0px 0px rgba(0, 0, 0, 0.14), 0px 0px 0px 0px rgba(0, 0, 0, 0.12);
}

.mdc-elevation--z1 {
    box-shadow: 0px 2px 1px -1px rgba(0, 0, 0, 0.2), 0px 1px 1px 0px rgba(0, 0, 0, 0.14), 0px 1px 3px 0px rgba(0, 0, 0, 0.12);
}

.mdc-elevation--z2 {
    box-shadow: 0px 3px 1px -2px rgba(0, 0, 0, 0.2), 0px 2px 2px 0px rgba(0, 0, 0, 0.14), 0px 1px 5px 0px rgba(0, 0, 0, 0.12);
}

.mdc-elevation--z3 {
    box-shadow: 0px 3px 3px -2px rgba(0, 0, 0, 0.2), 0px 3px 4px 0px rgba(0, 0, 0, 0.14), 0px 1px 8px 0px rgba(0, 0, 0, 0.12);
}

.mdc-elevation--z4 {
    box-shadow: 0px 2px 4px -1px rgba(0, 0, 0, 0.2), 0px 4px 5px 0px rgba(0, 0, 0, 0.14), 0px 1px 10px 0px rgba(0, 0, 0, 0.12);
}

.mdc-elevation--z5 {
    box-shadow: 0px 3px 5px -1px rgba(0, 0, 0, 0.2), 0px 5px 8px 0px rgba(0, 0, 0, 0.14), 0px 1px 14px 0px rgba(0, 0, 0, 0.12);
}

.mdc-elevation--z6 {
    box-shadow: 0px 3px 5px -1px rgba(0, 0, 0, 0.2), 0px 6px 10px 0px rgba(0, 0, 0, 0.14), 0px 1px 18px 0px rgba(0, 0, 0, 0.12);
}

.mdc-elevation--z7 {
    box-shadow: 0px 4px 5px -2px rgba(0, 0, 0, 0.2), 0px 7px 10px 1px rgba(0, 0, 0, 0.14), 0px 2px 16px 1px rgba(0, 0, 0, 0.12);
}

.mdc-elevation--z8 {
    box-shadow: 0px 5px 5px -3px rgba(0, 0, 0, 0.2), 0px 8px 10px 1px rgba(0, 0, 0, 0.14), 0px 3px 14px 2px rgba(0, 0, 0, 0.12);
}

.mdc-elevation--z9 {
    box-shadow: 0px 5px 6px -3px rgba(0, 0, 0, 0.2), 0px 9px 12px 1px rgba(0, 0, 0, 0.14), 0px 3px 16px 2px rgba(0, 0, 0, 0.12);
}