Grafana critical, warning threshold

Currently i am using Prometheus source and only manage to create the alert restrict and last with match $D > 1.50 || $F > 1.40 || $G > 1.40 with the value for multi demension. How we can setup the alert with the percentage 90% critical, 80% critical instead of set the value 1.50, 1.40 etc. Thanks.

Are there fixed upper limit values for D, F and G, such as 1.8 or 2.0?

it is not fix, but also set with value instead of percentage (warning, critical)