Your Image does not have the content class, causing the selector “img.content“ not to affect it
There is no use in wrapping it in a <center>-tag if you then declare it to float left
Width: 100% will never take effect, as you declared it width: auto !important before and important declarations can ponly be overriden by other important declarations - without regarding the fact that declaring the same attribute twice within a single selector is “stupid“ anyway as only one can take effect
Remove both width-declarations and replace them with the one from @Brogan, then it will work
PS: Avoid using !important whereever you can. If your attribute doesn't show any effect, you're likely to have either the wrong or a not precise enough selector.