Height with min and max in percent x auto

I have div , and its Height is 90%, but if I decrease the height of the browser the content exits out of div , how can I prevent it from exiting div ? I thought I'd use height-min:auto and height-max:90% but not scroll. but if I leave with height:auto , but for my content it would not be ideal.

Thetopinbluewouldbedivwiththesizeof90%thewhitepartisjustamarginbetweendiv,theblackpartisanotherdiv.Thephraseuptotheselectedwords(inblueintheblackpart)belongstodivazul.

Códigos

divAzul

.div4{background:-webkit-linear-gradient(top,#088fad20%,#00d5ff100%);margin-top:4em;padding:2em;border-radius:1em;width:100%;height:90%;}

DivPreta

.div5{margin-top:4em;padding:5em3em3em3em;background:#000000;border-radius:1em;width:100%;height:70%;}

I'maddingtheseimagestobetterunderstand:

withlowerheight:

withhigherheight: