how to fix mobile issues viewport and content wider than screen

Site URL: http://www.phoenix-consulting.ch

Hello Community

How can I fix the mobile issues of viewport and content wider than screen?

I have added the following css code in order to make the font on the mobile smaller.

If this code is not correctly can you pls help me and improve it so it will "satisfy" google.

Many thanks,

CSS

@media only screen and (max-width: 640px) {   
h1 { font-size: 20px !important; }}

@media only screen and (max-width: 640px) {   
h2 { font-size: 15px !important; }}

@media only screen and (max-width: 640px) {   
h3 { font-size: 12.5px !important; }}

@media only screen and (max-width: 640px) {   
h4 { font-size: 11px !important; }}

@media only screen and (max-width: 640px) {   
p { font-size: 10px !important; }}