Hello. I am looking for how to change text color and font for the lightning-radio-group standard component. The hooks work properly, but the rest of CSS doesn't work. And I haven't found hooks for text. Could you please help me?

Code that I have:
 

<lightning-radio-group  type="radio"
                        options={radioData}
                        onchange={handleRadioChange}
                        class="radio-group"></lightning-radio-group>

.radio-group {
    --sds-c-radio-mark-color-foreground: #9300EA;
    --sds-c-radio-color-border-focus: #9300EA;
    --sds-c-radio-color-border-checked: #9300EA;
    color: black;
    font-size: 16px;
}

.radio-group .slds-form-element__label {
    color: black;
    font-family: sans-serif;
    font-size: 16px;
}

My accounts have the Date field Activity__c. How can I figure out an average date between all these Activity__c fields?
I tried to use SOQL:

[SELECT AVG(Activity__c) FROM Account WHERE Activity__c != null]

But it shows error:

field Activity__c does not support aggregate operator AVG

My accounts have the Date field Activity__c. How can I figure out an average date between all these Activity__c fields?
I tried to use SOQL:

[SELECT AVG(Activity__c) FROM Account WHERE Activity__c != null]

But it shows error:

field Activity__c does not support aggregate operator AVG