You can adjust counter visual style, by modifying counter CSS file and by setting the charsImageUrl and/or markerImageUrl attribute value. The CSS file is located in /wp-content/plugins/counter/counter.css

[counter type="int" charsImageUrl="https://codeaid.uk/wp-content/plugins/counter/images/numeric_up_blackbg2.png" markerImageUrl="https://codeaid.uk/wp-content/plugins/counter/marker_small.png"][/counter]

[counter type="int" direction="Upwards" charsImageUrl="https://codeaid.uk/wp-content/plugins/counter/images/numeric_up_blackbg3.png"][/counter]

[counter type="int" direction="Upwards" charsImageUrl="https://codeaid.uk/wp-content/plugins/counter/images/numeric_up_blackbg4.png"][/counter]

[counter type="int" direction="Upwards" charsImageUrl="https://codeaid.uk/wp-content/plugins/counter/images/numeric_up_blackbg5.png"][/counter]

[counter type="int" direction="Downwards" characterSet="numericDown" charsImageUrl="https://codeaid.uk/wp-content/plugins/counter/images/numeric_down_blackbg6.png"][/counter]

[counter type="int" direction="Upwards" charsImageUrl="https://codeaid.uk/wp-content/plugins/counter/images/numeric_up_whitebg.png" markerImageUrl="https://codeaid.uk/wp-content/plugins/counter/marker_small.png"][/counter]